Google not only restricts film rental on Android devices regionally, but also excludes devices that have been routed. According to Winfuture.de, "Failed to fetch license for [movie title] (error 49)" is the error message that users with rooted devices get when they try to rent a movie with a corresponding device.
Google justifies this measure on the grounds that copy protection is not guaranteed if users have full access to their device. Google apparently wants to avoid potential problems with rights holders - the film industry would certainly not be happy if the rented films stay on the devices longer or even circulate. Whether Google will stick to this policy if more and more users make corresponding support requests is, of course, an open question. Perhaps Google will at least give the restriction a clear error message.