He voted against it because as one of the votes on the winning side he can later bring the bill up again for reconsideration. A losing Senator can't do that.
I understand that point of order, but Reid pushed this bill as a panacea. He wanted it to pass. That is evident. When it was clear that he lacked the votes to pass it, he voted against it to save face.
He knows damn well those Senators up for re-election in 2014 will have a tough road ahead. He didn’t want to be one of them.