Question: Don't kill me just yet, I'm asking out of pure curiosity.

Elements like `<section>, <nav>, <article>, <aside>` etc all seem completely pointless. Sure they make everything have its own little place (and seo'd)... but it **is** possible to over-organize things. There are some cases where things don't fit in any of the categories too. It also increases time spent trying to code these things. I just don't see any real purpose for moving to add these new elements.

What do we (developers and people who view the webpages alike) have to gain from adding them?

Answer: 
Allowing heading scope is the main benefit of `<section>` and `<article>`. See <http://diveintohtml5.info/semantics.html#header-element>.

Briefly: in HTML5, it’s much easier to mark up an outline of your document (which is useful for screen readers) without worrying about whether to use `<h2>` or `<h3>` or whatever (which gets really complicated when you include components in different places on different pages).

They couldn’t have done that with `<div>`s, because there are billions of web pages that have used `<div>`s and headings already, without necessarily intending heading scope.

Admittedly, `<section>` and `<hgroup>` would have been sufficient for this purpose.
The visual benefit of using the new HTML5 markup tags might be hidden from users but users may unwittingly benefit because these tags may have provided them with a better search result. I think once HTML5 becomes a standard the usage of these markup tags will become extremely important for your sites SEO.