Actually, I'm not sure if they cross-reference credit card numbers with itunes accounts or if its done through the credit card company; but I think this should be a service that credit card companies offer merchants... perhaps to help justify their massive merchant fees.
This is an interesting approach. Right now, credit cards don't get itemized receipts (afaik), just totals to charge to the customer's account.
For a service like this to be really useful to me, I would want itemized receipts.
Apple can do that because you can register an account online with Apple and they get your info (e-mail) by looking up your credit card?
A general solution would have to work with small businesses that don't have online services, which i assume being the majority out there.