Might be quite off-topic, but I want you to know that for international stuff Paypal has more value to me than Google checkout, as I don't have a credit card and Paypal works with my European bank account. It might be similar in several other countries, so that can be a reason for lower conversions with Google Checkout. Paypal in a lot of cases is my only online currency, alongside IDeal in the Netherlands (that works with my bank account as well).