When I worked at EB a few years ago, I noticed that the release date given by websites was always a day before it hit the store shelves. This means that the games are actually at the warehouses at the date given and are shipping to customers and retailers that day. The reason that that date is given, as opposed to the store shelf date, is for those who order it online. The release the date that it ships so that people are not crying, "where's my game?" when the date arrives. Otherwords, people would just go to the store on the day of release instead of ordering online (or maybe do both) so that they can get the game.
If you get the release date directly from the store that you want to pick it up at, they will often list the day after the websites list as when it will be in.
The only things I've ever seen hit shelves on the date announced as a release are consoles (and accompying launch game). Of course, that is because they ship out earlier than the date to make sure that the units are in stores when the lines begin to form.