Umm, they do have 100% functioning xinput support, they just don't have movement rebinding support. If I wanted to use WASD to play this game I couldn't do that, either.
I'm not saying that's any better but it is a bit different, as in, they did not really lie at all.
Honestly though, i really don't see how it bothers people so when games don't support controllers. It's really so very easy to use xpadder or joy2key. Although again, FS supports controllers perfectly, it just doesn't support movement rebinding for some weird reason.