How many people have both a 360 and PS3, not that many. So MS don't need to prove they are cheaper than Sony otherwise you buy a game on PS3. Even if you have both, you buy the DLC for the platform you own the game on, most people will choose one over the other because they prefer the controller, graphics or online service, not because DLC is 30p cheaper. I never even knew 800msp was officially £6.80, I'd certainly have thought harder about a few purchases if I knew 1200msp was ~£11. Although I buy prepaid cards at a lower price, ~£11 for an XBLA is a fortune.