It's indeed very strange. Not for VLC, because that program has its own codecs built-in and as everybody knows plays just about anything. But Mplayer also plays is correctly, and that player does use external codecs (to my knowledge). I have no idea why Quicktime doesn't seem to be able to do the same. I mean, H264 with mp3 sound isn't all that unusual, is it? I've seen this many time before with .mkv files and Handbrake is also capable of saving files using that format IIRC.