It's because of security reasons. I talked to the two guys working at GameStop yesterday. Since there is a great demand for the system, other stores were told by some unfortunate consumers (who did not preorder the system) that they were going to be at GameStop no matter what just to see if they could get any extra systems from the shipments. And that's unlikely because I was told that they are only getting a set-amount at the store for the people who preordered. If that's the case, then those extra people would get pissed off and do things such as stealing from people.
Years ago when the PS3 released, there was violence in the area I was staying at for college. There was a gun fight outside because someone stole a new PS3 from a person's car as he got out from the midnight launch.
