Medium-to-long term, we would like to add the option to pay by credit card directly through using a merchant processor, but it's something we couldn't implement in a week or two. Google Checkout is a way to let the majority of people start paying for accounts again quickly while we investigate other options; ideally we'd like to have a number of payment-processor options in the hope that one of them will work for everyone, but these things take time, money, and effort to implement and we thought it better to start with the easiest solutions and move up.