> If you're going to make the server clever, why not just make the server clever enough to return either an RSS feed or an HTML page depending on what it guesses the client wants?

There's no cleverness involved, this is an inherent part of the HTTP protocol. But Chrome still advertises full support for XHTML and XML:

    Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

But importantly, for audio/video files, that's still just serving static files, which is very different from having to dynamically generate different files.