I'm very surprised anyone goes near single player in any of the BF games - like many here I bought BF3 purely for multiplayer and have pre ordered BF4 for the same. I did try loading up the BF3 campaign once before deciding that although better than BF2's, it was still a rather poor show compared to its contemporaries..and have not touched it again.
I can see why they need to spend money on it though, as the console versions of BF3 in particular were crippled enough online (even smaller maps, no 64 player mode etc) that you need that single player experience to sell it.
I know they have separate teams to work on each aspect of the game but part of me does wish they would focus purely on the multiplayer and give up pretending they can do SP - we'd likely get an even better game as a result.