Few things - one, if it's a debit card tied to the account, it can be a major hassle, as debit transactions are totally different than credit transactions.
Two, forcing credit card companies to trace down/eat fraudulent charges raises prices for everyone.
Three, it costs $3-$5 for a replacement debit/credit card (some banks charge the individual for these as well)... Who's going to get to eat those costs?
Fourth, Individuals may have made the decision to purchase their $300+ system (and $60 games) based on SONY's claims of online multi-player. Even if you're not paying a monthly fee, you still paid for the service.