We have mostly hand me down systems in our household, and newer Nintendo DS'. When we do buy games for the DS' since they are the only ones we purchase new games for, I usually prefer online to read reviews...even though there is a GameStop right across the street from me, sometimes I make the purchase online if shipping is free.
I learned our library has a discount yearly rental card we can get to rent movies and games for one fee for the year (more affordable than online services). That would save gamers money. A great way to preview before you buy to make sure the kids really love the game.
Also hurting sales has got to be the advent of smartphones and tablets. The thing that drives me crazy is all the accessories, but I found with the iPad and iPod touches I could treat my kids to affordable or free games without parts and pieces to lose all over the house.