So what does XHTML offer that HTML doesn't? To me it seems like a transition that doesn't need to happen. Not to say it won't, but right now I usually code in HTML because that's what I learned in.
I think the biggest hurdle XHTML has is that it is a stricter markup than HTML; although that's not really a bad thing, it just makes it harder to learn. For example, <a href=""> and <A HREF=""> both work in HTML but only <a href=""> works in XHTML. Works isn't the right word. Only the lower cased variant is valid. <img src=""> isn't valid in XHTML whereas <img src="" alt="" /> is. Yes, it's probably a good thing to require an alt tag but there are times that a blank alt is the correct thing and I don't think we should be required to specify a blank tag.
edit... And think how many people use <a href="" target="_blank"> to create a popup link. That's not valid for XHTML. The workaround is Javascript, but that doesn't always work with popup blockers.