I know HD DVD wasn't ready when the 360 was released, but MS also said they didn't want to force customers to buy something they didn't really need either. Leaving that drive out also kept the cost down, but at the same time it could possibly have helped them win the format war. I really believe one of the main reasons Blu ray has done so well is because of the PS3 having a built in drive, regardless of the surveys that say close to half of the people who own one don't know that it can play blu ray discs.