Braintree certainly does recurring billing and it's pretty common in these scenarios for the migration to happen between vendors.
https://www.braintreepayments.com/tour/recurring-billing
Braintree even helped start http://www.portabilitystandard.org/ to help standardize the migration process.
That said, Google Checkout didn't do much in the way of recurring billing. The FAQ says it never made it out of beta. The vast majority of merchants appeared to just be selling the old fashioned way.