It was unnecessary, but it doesn't bother me as much as other changes. For example, for the theatrical SE's, they added a scream to Luke when he fell down the reactor shaft in ESB. Oooh, that bugged me so much, not the least because I recognized it as The Emperor's scream at the end of ROTJ. Thank God they removed that for the DVD's.
Anyway, now they shoot at the same time, and I think Han moves his head ever so slightly to avoid the hit. If he hadn't, he'd be dead. So Greedo's aim is not necessarily that bad, just his timing. His poor, poor timing.