They probably don't have DVD rental at all in your country. Netflix in the US/CA and Lovefilm in the UK were the only DVD/Bluray mailing service that I'm aware of. Once they were able to offer streaming internationally, setting up mailorder service probably wasn't even considered.
Maybe that's the perfect use case for subscription-based VPNs, renting DVDs from an American IP address... Hope it fits through the IP tunnel.