I still don't think it's going to be £50. Every game for the 360 is £49.99 RRP, but they never sell them at that.
The publishers might set a higher trade price, but someone will break that price and then the rest will follow. It might not be £30 at launch, but it'll be under £40 very quickly IMO.
But even then, it's cracking value. People will pay £15 for a film that you watch and then sits on the shelf, maybe you'll watch it again in a couple of months time. With a game like COD you'll play it for hours upon hours.