Why do merchants really need to store CC numbers? From the consumers' standpoint, there would be no difference if, during the first transaction, the merchant is issued some alterate key with which to charge the account. Each merchant would be issued their own key, so there would be no risk of a security breach spreading outside of the merchant.
One of the things you pay payment providers for is for taking on the risk of the higher levels of PCI compliance.
Depending on your payment provider, you will be however locked in and can't change anymore.
They need to store them transitionally to use them, but in general you don't really want to keep it around. The only legit reason is for subscription/recurring based charges, but if you're doing that you want to make damn sure you're not stupid with how you store them.
Stripe makes it super easy to never even see a CC, so I use them for a bunch of stuff, you can even do reocurring charges pretty easily. If you have any doubts about storing data safely, DO NOT DO IT.