And media files don't exactly compress... Odd.
Well, that's not true at all. Bitmaps and wave files can be compressed extremely well.
If you try to compress already compressed media, that's another story.
Ogg and png can be compressed a bit, but it's not worth the processing power for aac or jpeg.
ps: A good packager can also find similarities over different files and not compress each one on it's own.
So if the game was badly optimized and used the same resource in several files, that can make quite a difference.