Python/Ruby as mobile OS
In general it's all of these things. Memory, speed, and probably most importantly programmer familiarity. Apple has a huge investment in Objective C, Java is known by basically everyone, and C# is very popular as well. If you're trying for mass programmer appeal it makes sense to start with something popular, even if it's sort of boring.
There aren't really any technical requirements stopping it. We could write a whole Ruby stack and let the programmer re-implement the slow bits in C and it wouldn't be that big of a deal. It would be an investment for whatever company is making the mobile OS, and at the end of the day I'm not sure they gain as much from this.
Finally, it's the very beginning of mobile devices. In 5 years I wouldn't be at all surprised to see a much wider mobile stack.
I was wondering why smartphone/mobile device OSs are not written to allow dynamic languages as the language of choice?  iPhone uses Objective-C, Google Android uses Java, Windows Mobile uses any manner of .NET language.
What would be the reasoning behind a mobile OS being written in Python, Ruby, or any other dynamic language?  I understand that at a low level they would not cut it but C or C++ would be fine for that and Python, for example, could be the layer on top to interact with it.  I mean, there is Jython or CPython.
I was just wondering why we do not see more dynamic language support in today's mobile OS's.