Scalia was being ethical here is all. He probably didn't read the entire ruling, listen to all the arguments, before making public comments on the case in a speech. It left a question as to how impartial he would be on the merits. I think he could be, but he decided that his ethics require him to not hear this one. I applaud him for his decision, although I am worried about the impact.
It would have been better for him not to have been giving speeches on a case that was obviously headed his way though.