I found out that if you append "&fmt=18" to the end of a youtube url, you get stereo sound. I've been using it on my youtube vids for a while. And it seems like it does really make a difference. This is a supported feature of youtube:
To compare you can check out these two different versions of a clip from a DVD where Eddie Vedder does a cover of the Who's A Quick One with My Morning Jacket.
First the normal quality version:
Then the one with the tag:
Since we post so many vids in this forum I thought this tip might be helpful.