They're better off losing "fans" with short attention spans than paying customers. If your game isn't ready, your customers will quit and tell all their friends - as well as sites like this one - that it sucks. You lose a large chunk of your core market - many of whom will be hard or impossible to win back - AND your expansion market from bad word of mouth. It's a lose lose. You may be "losing interest" now, but if Warhammer is the best game out there come December, I suspect we'll see you in Warhammer.

Of course, the game still has to be good when it finally comes out, and it probably would have been better not to set a release window until they were more certain they could meet it. But more time can't make the final quality of the game worse, so it can only be a good thing.