I've honestly never thought about this at all, mostly because it doesn't make economic sense and it would cost too much and everyone would lose money and probably half a dozen other things I can't think of right now.
It doesn't make economic sense because then MS, Nintendo and Sony would have to start paying rent and employees to hock their wares instead of letting those costs go to someone else. Also then there is the fact that each of them would want exclusive deals. So that would be a MS in one mall, a Nintendo store in another and then Sony would be in a third mall. Look at Coke and Pepsi you can't buy both at the same restaurant. Then we move on to the fact that it doesn't make any sense from a developers stand point. As it stands right now I could walk into any store and think man that PS3 game looks so good I'm going to buy the system and then the game. But if I had to go into a Sony store to do this I wouldn't bother because I don't own a PS3.