We've had a couple of questions recently about semantic HTML. One was migrated to Stack Overflow, an the other is moving in that direction.

  * http://ux.stackexchange.com/questions/11329/page-title-h2-in-navigation-menu-markup-two-birds-one-stone
  * http://ux.stackexchange.com/questions/11841/what-is-the-semantically-correct-way-to-create-an-accordion-widget
 

Obviously, questions about how to write code to implement a UI are off-topic. The majority of HTML questions asked on Stack Overflow would not fit here. 

But when the question isn't about how to write HTML so that it looks right or works right in a GUI browser, but rather about the semantics of the markup, doesn't it qualify as an accessibility question?