They can fly Falcon 9 with cargo Dragons as well as unmanned Dragon 2 capsules many times before 2018. Demonstrated safety is hard to argue with.

There have been relatively recent failures with Soyuz launchers as well (though none with Soyuz FG). Russians have also been developing new things, both as upgrades to the Soyuz launcher and Soyuz spacecraft but also new developments. (Soyuz-2-1v and PTK)