We do monetize our users directly, 99% of them don't come from US. And I have to tell you the truth: it's incredibly difficult to sell to ppl in US. If you cannot provide $10 support for every dollar you take from your US customer he/she will not buy it and will request immediate refund. With such an attitude, we do prefer to reject payments made using US credit cards/paypal accounts to save our time and money. C'est la vie.