Schwarzenegger's a failure no matter whether he grants this clemency or not. If he does grant it, he's just a bigger failure. He won't have a second term no matter what.
The only reason I can see for him not having denied it already is a tactical one. Both a denial and the execution will most likely result in riots in L.A. so he needs to have the National Guard in place and ready to put a stop to it. It would be better to have both events happen pretty much at the same time so that he doesn't have to keep the Guard on duty any longer than necessary.
"He won't have a second term no matter what." I agree,look at the advisors he has now, all demo-rats.