I hope you're not suggesting that if you drink underage, you'll be okay with a sales receipt. Ignorant or not, you'd still get busted. In the alcohol scenario, both the clerk and the customer are at fault and each face consequences.
I don't know if it's "illegal" to sell a game before street date, but it is violating an agreement between the retailer and publisher that results in fines. Agree or not, Microsoft is exercising their right to protect their property and have the power under the user agreement to ban accounts. Assuming that copies being played before the official sell date are not legitimate (pirated, stolen, etc) is reasonable. The bottom line is the original poster knew the clerk was being shady, and the clerk knew better too. The customer was inconvenienced but got his account back, despite not even having a receipt.