The mixes--and the edits!--are very different. Not just in the obvious sense of different channel counts, but in the sense that they "feel" completely different.
I didn't notice the channel imbalance, but I was playing the redbook for the mono. Since that's on a server, I guess I can just fix the problem myself. But I'm once again scratching my head at how this stuff gets out there...when I digitize mono material via stereo recording, one of my finalizing steps is to choose either the left or right channel and duplicate it to the other. I don't want the record noise or tape dropout or whatever to be in stereo when the music isn't. I can't imagine I'm the only one.
(I'd just do one-channel mono WAV/FLAC but that can be a pain if I ever want to make a CD...which I never do, but still...)