There are so many factors that come into play when you go looking at gun & ammo sales.
1. Availability and how well something sells when it's put on the shelf of a LGS. I'm pretty sure gun store owners look at that specifically when it comes time to decide which guns to reorder.
2. Guns, & even ammo, are really luxury/amenity items; they are not typically "Necessary"; this comes into play when a potential buyer is looking at whether or not to buy a gun;
3. Being a luxury item, if the budget is best spent on bills, and for lots of folks, budgets are tight nowadays, well, less gets spent on such luxury items. The economy seems to be in a downward spiral as well. Maybe that is the biggest factor in prices falling; less available cash; and it's better to sell a thousand of something and make $2 each than it is to sell two of something for a thousand each. Think about it; although I'm certain that some will argue against, but when it comes to guns & related gear/ammo/etc, it's far better to sell 1000 guns than 2..
4. Politics drives demand as well. Get some idiots in DC trying to stop certain types of gun related sales, and you'll see runs. While you and I might consider our arsenal complete, younger folks, or those that were financially strapped before, but aren't now- might see it as time for them to take the plunge. As of late, it does seem that gun control, for and by politicians, seems to be political suicide; but that may change.
Right now, I wonder how much of the supposed slump is caused by a lack of spendable cash, and or by a lack of different choices behind the counters. However, with falling prices, it seems that the thing to do, if you can, is to consider buying what you feel you need, and buy it while the prices are lower. We are always just one "bad" event away from a rush, or so it seems. In other words, now, while prices are lower, is a good time to stock up on things like ammo, or to pick up that gun that you did want before but didn't have the cash for..