On the other hand, marriage itself brings up its own set of problems. Would marriage between people of the same sex be OK? Odds are that's a bomb that Blizzard doesn't want to deal with. And how would divorce work? A formalized ingame marriage could be as messy as marriage in real life if not dealt with properly.
Later in the thread, Nethaera shows up to turn the conversation from RPing in general, and I agree with her-- we're already playing characters here, and there's nothing wrong with doing something cute like this to let two people playing the game show a little affection for one another. But unfortunately, odds are that this is a little too messy an issue for Blizzard to put much work into.