http://usability.com.au/2013/01/headings-who-needs-em/

Quote Originally Posted by article
This is a story about web page headings and sub-headings: A story that tries to look beyond the absurd distinctions that are sometimes made about the usability and accessibility of web content, to ask who needs headings and why.

Imagine, if you will, a web page containing a 5,000 word article; a large slab of text with many sentences and paragraphs. Most, if not all, people will find this article easier to read if it is broken up into sections, each identified with an appropriate heading or sub-heading, and for people with disabilities it can be especially important. This is the starting point for our discussion of web content usability and accessibility.
The main point of the article, though, seems to be that sometimes the WCAG2 level requirements (A, AA, AAA) are a bit strange. He gives an example of what's needed to conform to level AAA with headings, and then for just A (the lowest). For example, breaking up a 5000-word essay with properly marked-up headings with unrelated words (such as <h1>jibber-jabber</h1> and <h2>heading!</h2>) will count as satisfying level A conformance. It's only up at level AA that the headings actually have to have meaning. That is lawlz.

But anyway, a fun read. Enjoy.