Given US gun homicides are around five times as high, I'd suggest triumphalism is a little inappropriate.
Percentage of homicides with firearms: Australia 16%, USA 39%.
Australia firearm homicide rate: 1.8 per 100,000
US firearm homicide rate: 9.1 per 100,000. Nearly five times as high.
It's great that US crime in general has been falling, and gun crime along with it. That's due to a lot of factors beyond the firearms context alone, including a drop in population of 'criminal age' males; plus the drop in demand for crack and other factors, like smarter policing.
Edit. Beyond all this, remember the context of this thread. It's the Sandy Hook massacre in which 26 people died. AR-15 style weapons are behind many of these attacks, here and elsewhere in the world.
Banning the AR-15 might only save a hundred lives a year - like these elementary school kids and children at the cinema in Colorado. Some AR-15 fans might suggest that 100 or so people dying isn't much of a difference, given the loss of a vital right. I think having a few dozen more kids alive is a good aim, and I'm glad to see once-NRA supporters endorsing that view.