"application / xhtml + xml", why bother?
Nobody in their right mind really cares whether their web page is ‘text/html’ or ‘application/xhtml+xml’. And why should they? I mean my pages look the damn same either way. The heavens don’t open up and God himself doesn’t bestow me with something along the lines of eternal life when I set my web page mime types to ‘application/xhtml+xml’.
That's not true. HTML pages served as text/html and using the proper DOCTYPE need never be modified.
If you write bad XHTML then it will break when served as XHTML, that's not a spec problem, nobody forces anyone to use XHTML.
If your poodle explodes in the microwave, it does not mean there's something wrong with the microwave. It just means it's working.