I work for a major retailer and not only will our registers not allow for cd's, dvd's, and video games not allow for sales before the street date, BUT our receiving personnel never even unpack the boxes of street dated materials. In other words, the music, movies, and games that are street dated aren't even brought close to the sales floor -- they're locked up back in receiving.
If all retailers would just have systems that won't allow the sale (such as mine) then alot of these early sales could be stopped. You'd still have mom and pop stores who release early to keep their customers happy and compete with the big guys.
BTW, I don't work for Wal-Mart but that's pretty close. If you're a cheapskate, we sell new video games at $54.xx instead of $59 and the collectors editions of both Halo 3 and CoD4 I've picked up at my store for $64.xx -- saving more than $5!
On another note, going back to leaking games early, I don't care too much. Games like CoD4 being leaked early do frusterate me because you rank up and have an advantage if you get it early. But I'm still skilled enough to do pretty well and do so ultimately it's not a big deal.