Big picture questions regarding Django, Java, Python, HTML and web-site development in general
From what I read, ROR tries to do everything for you behind the scenes and so therefore is slow and unscalable (and overhyped and not ready for prime time).

Well, first of all, you shouldn't believe everything you read on the Internet:

I wouldn't say RoR isn't ready for primetime. RoR, like any tool, has its uses. If you're building a site like Twitter, maybe Rails isn't the best tool (as Twitter found out). While everyone thinks they're building a high-performance site, most developers aren't, and Rails will probably be suitable. Furthermore, Rails can scale, and a lot of work has been done to improve that situation even more.
The reason Rails sometimes has performance issues is not because it tries to do everything for you -- it's more because of the nature of the Ruby interpreter itself, which (until Ruby 1.9) was rather slow, and still isn't even as fast as other interpreted languages.


And the first thing that surprises me about Django, is that there does not seem to be any innovation to speak of regarding actual presentation. All the innovation would concern database issues, business logic, reusability of code, etc - but not actually anything new regarding innovative visual controls or graphics for a web-site.

Yes, but that is the innovation. Prior to frameworks like Django and Rails, a lot of that backend work was done by hand. Django frees up a developer's time to work on more application-level features.

And I would have thought previously that html might be analagous to assembler, so a conventional application developer from years past might know and occasionally even use a little assembler, but generally would hardly ever use it, whereas from what I can see, html (and also CSS and javascript) still have to be mastered and written continually by every web developer, whether they're using Django or anything else. Is that a true statement?

Yeah, pretty much. Nothing better than HTML, CSS, and JS has presented itself. While I agree that in some ways, HTML seems "low-level" in the same sense that assembly language is low-level, I think most would agree that, relative to problem domain, HTML is much nicer to work with.

Would Django be used in conjunction with something like Flash or even Java applets?

You can. Flash and Java are just embedded in HTML pages, and Django spits out HTML, so that's certainly possible.

Are there in fact complete websites written solely in Java, perhaps using very high level Java API's? Why would someone say (as I read somewhere) that they despised Java so that is why they had gotten into Ruby on Rails and Django.

In addition to applets, you can write a backend in Java (Java Server Pages, for example). I think most web developers who have worked with both would agree than Ruby and Python are much nicer to use than Java. Java web frameworks are kind of a pain, Java lacks a REPL, Java has a separate compilation step... Java is also statically typed; you can argue all day about the merits of dynamic typing vs. static typing, but Rails and Django both take advantage of Ruby's and Python's typing and introspection capabilities to make a lot of code less verbose than that of Java. (Whether that makes Ruby and Python better than Java is subjective.)

And regarding Python (and also PHP) what is the justification for their existence? First of all, Python is much, much slower than say C++, being interpreted. Why are websites written in Python or PHP - is platform independence the sole issue here. I am incredulous that application development is much faster in Python than C++ (aside from the garbage collection issue - is that what the primary reason for Python is - garbage collection.)

Performance isn't everything. Almost everyone wants to think their code is performance critical, but that's often not the case. As noted in a few other answers, most web apps are I/O bound anyway -- they're either waiting for database access, or waiting on the network, and both of those types of operations are orders of magnitude slower than CPU-intensive tasks, even with slow(er) interpreted languages. Furthermore, a lot of processing in web apps takes place on strings, and string processing is much nicer in Python or Ruby than it is in, e.g., C or C++. Python and Ruby are also more concise languages, and both offer a REPL which can shorten development time. Plus it's easy to write C extension modules in both Python and Ruby, so if you really, really find a code path that calls out for optimization, you can always drop down into C if you want.
Garbage collection is a plus, though.
I am trying to get a handle on the state of the art regarding web site development and have several questions. Maybe I'll end up finding most of the answers on my own.  I come from a background of C++ and Windows development, and generally I am befuddled by what seems to be the ad-hoc nature of web development.
I focussed in on Django, after online research of it and Ruby (on Rails).  From what I read, ROR tries to do everything for you behind the scenes and so therefore is slow and unscalable (and overhyped and not ready for prime time). So I have gotten into Django - downloaded Python and Django, the source from a complete Django site, got it running, and so forth.
And the first thing that surprises me about Django, is that there does not seem to be any innovation to speak of regarding actual presentation.  All the innovation would concern  database issues, business logic, reusability of code, etc - but not actually anything new regarding innovative visual controls or graphics for a web-site.  When you build a Django view or template, it will still be making extensive reference to html from what I can see (And presumably also Javascript - but I haven't actually even seen any Javascript in Django templates yet.)  
And I would have thought previously that html might be analagous to assembler, so a conventional application developer from years past might know and occasionally even use a little assembler, but generally would hardly ever use it, whereas from what I can see, html (and  also CSS and javascript) still have to be mastered and written continually by every web developer, whether they're using Django or anything else.  Is that a true statement?
There is one site in particular that would to me as an end user represent the state of the art for web sites and I would be curious as to what the foundations of such a site might be.  That site is chess.com,  and there are all sorts of facilities for playing chess online with other users, user customization of their account with various graphical effects and so on. Is it most likely Java applets they're using for a site like that? How relevant would Django be for a such a site.  Would Django be used in conjunction with something like Flash or even Java applets?  Also when a site like chess.com is ported to a mobile device, what is used to write it - the same development tools as for the desktop or something completely different (Yes, I have a lot of catching up to do.)
Are there in fact complete websites written solely in Java, perhaps using very high level Java API's?  Why would someone say (as I read somewhere) that they despised Java so that is why they had gotten into Ruby on Rails and Django.
And regarding Python (and also PHP) what is the justification for their existence?  First of all, Python is much, much slower than say C++, being interpreted.  Why are websites written in Python or PHP - is platform independence the sole issue here.  I am incredulous that application development is much faster in Python than C++ (aside from the garbage collection issue - is that what the primary reason for Python is - garbage collection.) 
So anyway, a bunch of newbie questions - will probably end up answering most of them myself if they're not answered here. Maybe they're relevant to someone else though.