I would be curious if that was actually covered under warranty at all, given the life of a truck is usually to axle, but given there is no axle to grind to, it could be said that the truck was skated for its intended purpose and that was its life.
On the other hand, they might replace it just because they are a new company and are trying to have a better image, especially with some of the issues people have been having.
At least if nothing else, you have a spare baseplate and spare truck to use with the next set, if you get another set, that is.