[entropy_]

Probably not, most, if not all, non-compliant XML/XHTML is either written by hand or by very bad generation tools. In the case of HTML/2 it's a protocol that needs to be implemented by browsers and web servers and there are only so many of those. In the case of XML/XHTML any person throwing up a website or sending a document does the generation with a different set of tools(or by hand)

[jimktrains2]

I've seen tons of computer-generated terrible xml. It's in use in so many custom API's I can't even describe to you. Poor escaping, nesting, &c.