The article "In Medical Triumph, Homicides Fall Despite Soaring Gun Violence" http://online.wsj.com/article/SB1000142412788732471250457813... from December 8, 2012 provides some perspective on falling absolute numbers (and thus a falling rate) of gunshot deaths. "Crime experts who attribute the drop in killings to better policing or an aging population fail to square the image of a more tranquil nation with this stat…
Your link is behind a pay wall for me and I don't have time to completely analyze how they're justifying their spin, but according to the Bureau of Justice, non-fatal firearm crimes have indeed been falling for the last 20 years, so, no, it's not just a product of improving treatment of gunshot wounds:
Nonfatal firearm violence declined from 1993 through
2004 before fluctuating in the mid- to late 2000s.
[http://bjs.gov/content/pub/press/fv9311pr.cfm]As this is a well-known trend, I'm pretty sure anyone who wants to can find lots and lots of citations.
Moreover, this should be obvious to anyone who has participated in public society for the last 20 years. Decreasing crime statistics, including gun crime, aren't fool's gold. Crime is down. Society is getting gentler.
Twenty years ago I was 15. Gang violence dominated the news. Hard gangsta rap infused pop culture and music and it carried with it a true dangerous edge. Now culture is changing. Electronic music is popular. NBA basketball players dress up to look like Carleton Banks for press conferences. Internet culture, reddit culture is taking over. Kids spend all their time watching silly YouTube videos and playing iPhone games. There is far less free time for roving bands of aimless punks to get up to mischief. My teen-age son and his friends are incredibly nerdy and gentle and I've noticed this throughout the generation.