I am an avid gamer as is my husband. It's how we fell in love!
That said, I love being able to trade in games that I have completed so many times that I could play blindfolded! I love Gamestop and make weekly visits there even if it just to visit with the employees and not buy a game. They know me, my husband and my son just by our voice so that even when we call ahead of time to see if they have a certain game in stock we don't even have to tell them who we are, they just say they'll have it ready for us when we come into town.
If Microsoft and/or Sony decided to make their consoles solely based on online purchases it could potentially ruin so many pre-owned gaming stores, not to mention any store that sells video games. Many businesses would lose a large amount of their profits! I would not buy the 720 if all I could do was buy games online.
I have bought games via the X-Box 360 Marketplace but only because they were hard to find games or indie games (such as Portal... I did not want The Orange Box only Portal so I bought it with Micro-Points and I've bought Orcs Must Die and A Kingdom for Keflings for my son because because they are not available on disk).