I haven't been to a Gamestop in a while, but I would guess Wii was moved to the back because they don't have any trouble selling them. People likely come in looking for one all the time. Putting PS3 in the front is Gamestop's way of increasing awareness of the product in an effort to sell PS3s. Retailers don't really make money on hardware, but if the hardware doesn't sell then the software won't either. Wii doesn't need to sell any better than it has been for them to make money on it.
And also, Gamestop sucks. What the hell were you doing in there or even looking around? Go buy a pizza or something and keep the hell away from that evil corporation before they end up buying you out and investing in your mom's stocks, effectively taking over her operations.