The rapid fire coupled with long intervals before the need to reload, suggesting little kick and large magazine capacity. That is what makes these weapons different from hunting rifles.
Yes, he beat his grandmother to death, but fat chance doing that to four firefighters in the open. And while he could have gotten an assault weapon even if they had been banned, it would have been considerably more difficult.
Which to me is an advantage to gun control law. It doesn't make things like this and Newtown impossible, but it does make them more difficult to accomplish and potentially less deadly.