If you buy several months of WoW playtime from Blizzard, they don't take all the money at once. I guess folks would balk at that. But neither do they set up a standing order or direct debit to take the money. I wish they had, after all, one can cancel a direct debit or standing order (some bank staff will try to tell you different, but the truth is you can cancel a direct debit from your account).
No, what Blizzard get one to do is pre-authorise a slew of payments, kind of like giving them a pile of post-dated cheques. Cheques that you can't cancel. When I asked them to cancel the payments they assured me that "No more payments will be taken once the current period of subscription is over."
In other words, despite my request to cease payments, they will carry on taking the money just the same as before. The only way I can stop them is to cancel the card.