Wait... I just noticed this:

[XHTML] never took off on the web, in part because in a website context so much HTML is generated by templates and libraries that it’s all too easy to introduce a syntax error somewhere along the line; and unlike HTML, where a syntax error would still render something, the tiniest syntax error in XHTML means the whole thing gets thrown out by the browser and you get the Yellow Screen of Death.

This confuses me; don't you want to make sure you are always generating a syntactically valid document, rather than hoping that the browser will make something suitable up to work around your mistake?