Come to think of it, there are not that many games made solely for on-line gaming (I could be wrong); WOW does come to me as an all on-line game. The whole Call of Duty singleplayer was superb and the multiplayer experience as rewarding. Quake 4 is a combination of both multiplayer andd singleplay. So is Crysis.
To Rujman: I didn't get you right; are you suggesting an immerse singleplayer such as Half-Life 2 and later on a completed expansion to add on multiplay, like TeamFortress (ofcourse not cellshaded, but more developmental focus on multiplay)? Cause if that's your point, it could give the community time to help Epic develop maps, mutators etc.