And you make a good point about html being stretched to have to define both document structure and application interface – often on the same page.

Yes, HTML is relatively poor in meaningfully descriptive tags, but we do have pretty good patches for these problems in the form of Microformats and RDFa.

But I disagree with your closing point on Accessibility over Semantic Markup. This may very well be academic as I cannot think of an example of semantic markup hindering accessibility – indeed I firmly believe that semantic markup is the one true route to real Accessibility.

I reckon that with web development in general, you should try to avoid going for the moving targets of optimising for specific user agents (* okay, we all have to cater to the whims of IE to some extent), and instead adhere to common principles that will work in the long term. User Agents will change and develop, and they will do so (I’d hope) in the direction of semantic markup.

Making your html as semantic as you can (possibly with RDFa and/or microformats) opens up your content to all kinds of as-yet uncharted possibilities.