Because there's still the illusion that used games are cheaper.  Also, people throwing their in-store credit onto their Edge cards are slaves to buying their games at these stores.  It's where their money is.

US prices:
 
Best Buy
 
Gamestop

this just reminded me that SSFIV was 40$ o-o  
 
THAT MEANS I GET JUST CAUSE 2 EARLIER YAY! :D

Why do people shop at Gamestop because I just purchased new copies of Persona 4 and Call of Duty WAW for a total of $40 which is how much 1 of those games cost at Amazon or Best Buy.  Plus when I bought it the guy at the counter was actually able to compare the pros and cons of Persona 3 and Persona 4.

Right now a lot of new games are cheaper than pre-owned games because gamestop is apparently having some huge sale. 

The second-hand games market is a total travesty at the moment. You receive pittance for a game maybe a month old, which they then sell on for a massive profit. Copies of new games which are pre-owned are sold for a couple of quid less than retail, which many people would pick over the slightly more expensive new copy so that they earn more or less double for a single game. This means less stock of new games and a huge pre-owned section. Along with piracy its a pretty major problem.
 
Edit: I haven't proof read this and I'm tired.

I paid $50 for John Voight's copy

I get all of my games from Amazon and Goozex. I've probably spent a grand total of $50 in the last 6 months, while I've purchased dozens of new games.

" I paid $50 for John Voight's copy "

You know what's really funny? Rock Revolution software + drumset is $10 brand new.
 
Yeah.