From the XFM Web site:

Salient points, in order of increasing importance*:

(1) XFM’s browser detection is correct

(2) XFM understands that codecs are the stumbling block in streaming media, not browsers or operating systems

(3) XFM understands that a variety of apps are available and that I could have one that works

:.  XFM doesn’t tell me whether or not my computer can play the stream, it lets me decide and press the “play” button.

[* - Note: maybe (2) and (3) should be reversed….]