First, there were games like Starcraft and Diablo, which allowed a group of friends to play on a LAN together with only one copy of the game via the Spawn feature. And God saw that it was good.
Then, there was Diablo II. It lacked the Spawn feature, but players could still choose between single-player, LAN, and Battle.net, so God saw that it was not as good as before, but still good.
Then, there was World of Warcraft, which was basically a Diablo game (complete with an NPC named Griswold and an item called the Butcher's Cleaver), but with a much crappier combat system, sillier quests and items, cartoony graphics, and the ability to play as a species other than human. It didn't allow offline play, but it's an MMO, so God was like "Well, what do you expect?"
Then, there was Starcraft II, which did not feature LAN play at all. Players were restricted to single-player and Battle.net, and God, or at least the South Koreans, saw that it was NOT good, and continued playing Brood War.
Now, there will be Diablo III, which does not even offer a single-player option. Everyone will have to play on Battle.net, because apparently, Bliz has stopped paying attention to the Command & Conquer franchise, which died a horrible, gruesome death when Tiberian Twilight tried the same idiotic scheme. Bliz has apparently also forgotten that Diablo and WoW are not the same thing, and a lot of Diablo fans look down on WoW. And God said "Screw this, I'm gonna play Hellgate London"