in reply to
Larry vs. Joel vs. Ovid
Not only is the browser the problem, but the web server is. Remember back when PNG's came to town. You didn't have every webserver add image/png automatically. You didn't have every sysadmin find out about it. It took a while, and there's some out there that don't have that. Right now, BZIP2 format isn't being recognized, and is sent application/octet-stream or, even worse, text/plain! (Try pulling a Kernel, and it spews all over your screen)
IE's being mistrusting of the webserver, rightfully so. But then it hides that fact, not letting programmers know about it. Naughty IE!