as a gift card buyer rather than a credit card subscriber (I refuse to go into debt over any game) I personally look at the items given by gift card purchases to be sort of a monthy gift type item for me, basically if I like the gifts I look forward to them and want to buy the gift cards more, if I don't like the items then I question if I want to buy any more or play more... that is the thing with gift card players, they can stop paying at any time but likely will keep playing as long as they are kept happy... on the other hand yearly subscription buyers have already paid upfront and I don't know how likely it is for them to purchase a second year's subscription after their first year has run out. In any case, Wizard101 should do what is necessary to retain and hold onto its revenues however players choose to pay.
I have noticed that a lot of players wish they could buy gift cards in their area, so it does seem that players do want to buy the cards. Once again, I prefer to buy the cards over spending half as much through credit card subscriptions cause I don't like debt on my credit cards. I don't like oweing anyone anything, just don't like it.