1) I only see single-player games on that list, with the exception of STO. A comparison of MMO player statistics would be more relevant.
2) This is only indicative of players using Steam as their vehicle for playing. Even though I purchased through Steam (for their preorder exclusive), I prefer using the stand-alone client, not the Steam client.
Agreed on both. I personally have a Steam Account, but I bought STO through GameStop. The only game I launch through Steam is HalfLife2.