Agreed. I rushed that part of the comment so as not to miss a train and failed to mention just how limited the installed base of OSS users actually is. (I meant 'all Unixes' when I said 'everywhere', but of course that was wrong: as you mention, the largest Unix installed base these days is MacOS X.)
Using gstreamer would be a good idea, but a lot of people ran scared of it after the gstreamer 0.10 transition, in case it transitioned again and perhaps because the 0.x version number promised a transition. I don't know why they don't just drop the zero and redesignate it 1.x (so we'd be at 1.24 now, or something like that).
It was years before I had more than one or two users of gstreamer on my system, and it wasn't until I installed KDE4 that the majority of my media playback started to use gstreamer. (Maybe people doing recording and manipulation would have been heavy users earlier, I don't know.)