hrm... well Karl did mention that he made the file at youtube's framesize, 320x240 I think, so maybe they did less compression to the file, than the ones you did, that is the only other thing I can think of, all of the sites that allow audio and video, further compress the file for better streaming which if you have a larger file, with big pictures will mean the file is compressed for stream which would degrade the audio as well...
hope that makes sense....