Look, go ahead and serve up “XHTML” as text/html. Really! So what? Yes, yes, if you actually served up your page with the right mime type so that it actually got parsed as XML instead of invalid HTML, your website would completely fall over. But hey, no worries! Fortunately, you’re not actually using your “XHTML” for anything that HTML 4.01 can’t do, so you can afford to blithely ignore the standard. Unlike, say, Jacques “The Hardest Working Man In Show Business” Distler.
So write some manifestos! Slap those XHTML doctypes at the top of your pages! Go nuts! But before you do so, take some time out to be thankful that there are hundreds of bright, hardworking, underappreciated coders who are designing browsers to clean up after your mess, just as they did for the table/spacer-gif jockeys of yore. I don’t think that’s too much to ask.