Sorry, but you’re mistaken. The parent never brought up IE - he was referring to the fact that when serving XHTML with the correct mime-type (application/xhtml+xml), any error causes the page not to render at all. This behaviour is intended per spec and was the same across all browsers, not due to lack of support. It’s called “draconian error handling”, consequence of being XML, and was a major factor in the death of XHTML.
The death of XHTML was brought on by the then crop of kids who don't want to understand how computers work and want it all done for them with someone else's code cause computer science is too hard and they'd have to think and thinking is too hard.
While I often hear this "draconian error handling" about XML/XHTML by such people who then complain that a language compiler is just as draconian and real programmers complain when it's not and doesn't catch their every little mistake.
It's this lack of education and drive for the pursuit of knowledge and understanding that caused XHTML to fall out of favor and no other reason.
That's all well until you have external content (e.g. blog with comments or blog roll headlines). Many an enthusiastic Web author in the 2000s migrated off XHTML again. Not because getting it right is too hard (each fix for each problem is quite straight-forward and often trivial), but because when you have the choice between having a completely broken page/site until you have time to log on and fix it and having a miniscully broken part of a page that's easily ignored by a visitor, then the idealism was just too bothersome. Unfortunately, that's human nature. Also see: rms's principles as exemplified by his life-style and how many follow his example perfectly.
