They're planning to change that, though.

They're working towards charging patrons as soon as they pledge, and then on the month anniversary of that starting-to-pledge. Or if someone has the "pay per creation" model, charge them as soon as a creation is posted. Thus the fee added on each and every pledge.

Since the whole point of Patreon was to support multiple creators with small recurring payments without having to pay transaction fees for each payment, I really don't get what they expect to happen.