> The pursuit of the semantic web has changed in the era of HTML5, which represented a rejection of XHTML — to me, a seemingly bizarre rejection of having to write well-formed XML as somehow being unreasonably burdensome.
This is a classic "worse is better" situation. HTML5 may be "worse" than XHTML, from the standpoint of extensibility, namespacing, code cleanliness, and so on. But HTML5 is simpler to write for people who knew HTML4, and easier to get right using the one ubiquitous web development practice: staring at the rendered result in your browser, which every web developer has installed. So it's "better", and ends up winning.
This is a classic "worse is better" situation. HTML5 may be "worse" than XHTML, from the standpoint of extensibility, namespacing, code cleanliness, and so on. But HTML5 is simpler to write for people who knew HTML4, and easier to get right using the one ubiquitous web development practice: staring at the rendered result in your browser, which every web developer has installed. So it's "better", and ends up winning.