I can see either side of the Bisping Sonnen argument. After rewatching the fight 3 times I can say it could have gone either way, but Sonnen got the nod because of the takedowns and punches on the ground.
Bisping found a position that he could keep Chael in and he kept going back to it, but he didn't do much when he was in that position. On the feet Chael looked wild and Bisping looked sharper, but they both were able hit each other around the same amount of times.
No matter who it went to, it wouldn't have been a robbery. It could have gone either way and a split decision for Sonnen sounds about right to me, although this is about as close as they come.