True, but even in the U.S. where guns can be obtained legally there is still an illegal weapon trade going on. Then again, anything could be traded illegally, even a basket of apples, although I can't think of a reason why anybody would, and it would be a lot harder to get that done illegally, but still...
If you take into account though that, in countries were guns are outlawed, most people who get killed by a gun, were mostly already in the illegal circuit themselves and were a threat to other criminals, and in the criminal world the law of the jungle applies (eat or get eaten). People not involved in the criminal world have overall little to fear... Shoot-outs are rare, and the innocent people who did get shot dead were in the recent events mostly mistakes (but if they had a gun, they'd be dead either way, since the killers were assassins trained to be invisible till the very last moment, and nothing can save you from those kind of killers). These mistakes are risky for criminals, and a load of them got them in more trouble than they already were, so I guess criminals will be more careful... if it's not out of ethics, then it's out of their own security.
But then again... 100% security can never exist. Illegal stuff, whether guns, drugs or something else, will eventually always find its way into your hands if you know where to look. And crime-fighters know it.