So, the series has no multiplayer. :shrug:
*but there are no other games like either of them (1,2,3, and NV)
Fallout is about desolate isolation; its just not a buddy game, and running around the wasteland with buddies isn't really conducive to a sense of dread and loss at all that was destroyed, and that feeling of being alone.
*And besides.. no one wants this...

http://i271.photobucket.com/albums/jj125/Gizmojunk/FalloutMMO.jpg