I can see a case to be made for it being a close fight, but I would really question anyone's ability to judge a fight if they argued that diaz won... the first two rounds, diego took diaz down at will and basically kept the fight even on their feet the little time they were there... diaz landed nothing significant standing and his best strike of the whole fight was an upkick from his guard...
on the ground, diego maintained complete control in the first round and lost top control with 1:15 left in the second round, nothing diaz threw from the top landed... diego also had a decent armbar attempt though from the angle shown, it was difficult to see how sunk in diaz was... diego's striking wasn't fedor'esque, but they were scoring blows.... the best thing I can say about diaz's ground game is that he avoided the big blows, which I don't give actual points for...
the third was a pretty even round with diaz better able to keep the fight standing, but still unable to land anything significant... on the ground, diaz had a beautiful kimura attempt that was instantly rolled out of by diego... diego also resumed top control and there were some pretty even exchanges of elbows...
I can see 30-27, I can see 29-28, but I don't see any way in which a judge could have scored the fight for diaz...