That is, in NO WAY true! I've been playing bfbc2 alone for a while, since none of my friends owned the game, and i had a great load of fun.
I found it that i don't want to play cod without someone playing with me, because then I stop being so competitive and starts playing to have fun. xD
But i agree that BF is FUNNER with friends. But it can be enjoyed very much, even if you are alone.