DeathInMyEyes
DIME
That's only assuming that everyone is connected to the internet or money for a gold account which one needs to use the online mode on the 360. It's better for a game to have inherent offline replay value rather than have a good portion of its replay value dependent on internet connectivity. Just look at MK9 which has both great replay value and online and is loved for it.
It has great offline replay value, unless you refuse to travel and/or you're a social reject with no friends.
Also, MK9's offline singleplayer is ass for replayability, and the online has shitty netcode, which hurts its multiplayer replayability. So SC5 > MK9 in multiplayer replayability. They're about equal when it comes to singleplayer replayability.
But fuck singleplayer.