I can understand people wanting to ban stuff that could theoretically be used for crime, but that's a really big slippery slope to go down. The next logical step would be to ban rifles and shotguns because they blow through body armor like it's not even there.
According to wikipedia, those 2 guys were the only people who died during that incident. That's fairly impressive. It ended quickly too. It went on for less than an hour, and it usually takes 59 minutes for the police to respond to a 911 call.
The idea is to make it more difficult to carry out a crime. Most people are extremely lazy, so even the most basic roadblocks will stop things from happening. That 2012 voter ID thing is a great example. Democrats were saying millions of people would be unable to vote if photo ID was required for voting, and they were probably right. Are people so retarded that they don't have the ID required to open a bank account or get a job? Probably. Putting the same restrictions on gun purchases might make it difficult for profoundly stupid people to obtain weapons. You'll never stop the people who are cold and calculating, like those hollywood shootout guys, but simple barriers might deter the more lazy criminals. One can look at Canada to see how this works. Most people think pistols are illegal in Canada, but that's not true. All you need to do is take a course on pistol safety, fill out a form, wait a month or two, and you can buy as many as you want. How many people actually do it? Very few. This is why Canada doesn't have many shootouts.