Xenoblade Chronicles is available for rent on Gamefly, a reader informs Joystiq. We checked and, sure enough, it's there. "But it's supposed to be exclusive to the Nintendo Store and GameStop!" you say. To that ... well, we don't really have a snappy retort because we're just as flummoxed as everyone else. Whatever the cause, it seems being able to rent the game has created an exception.
Regardless, if you don't feel like paying a premium to try out the excellent RPG, and you happen to have a GameFly account, give it a rent. As of this writing, Xenoblade Chronicles is listed as "available now."