Microsoft's problem should, indeed, be with the retailer. Unfortunately, MS instead banned the OP, who didn't do anything at all wrong. He bought a video game. He didn't have any obligation to enforce MS's street date. That's why your analogies using illegal conduct are bullshit. In those cases, the person doing the buying is breaking the law.
You act as if MS had no choice, but of course they did. There was nothing inevitable about the ban. It wasn't out of MS's hands. I don't know why you give them a free pass. You say he should have known he was risking a ban, but that't not true. As I have posted several times, the entire issue is contrary to MS's stated policy. MS in the past said:
"If a user happens to purchase a legit copy of Halo 3: ODST early, then our problem is not with the user but the retailer who broke the street date. Those individuals will not be punished."
And yet here we have a use who purchased a legit copy early, and was punished. If MS has changed their policy, they ought to act least have the common courtesy to tell us.