Speaking about Blizzard, I heard from a post by one of their employees on the official boards that only 5-10% (I forgot which) bought Diablo2 for battle.net. You can play it on a LAN but I doubt that the total multiplayer component is much larger than the 5-10% of battle.net. Note that this is already Diablo2, easily in the top 10, maybe even top 5, most successful multiplayer games in PC history. Other Blizzard games have around the same online penetration.

Besides, succesful multiplayer games are mostly of the same genre, clickfest. Warcraft3 is mostly an exercise in clicking speed. There's actually a program out there that measures clicks/time and the faster clicker wins a huge majority of the games. I already feel that RTW, in the tactical battles, is somewhat dumbed down compared to MTW. To be successful in MP, it has to dumbed down further, something which I don't like.