Pretty sure it does have a fan:
But yeah not as good cooling is the only reason I can think of for it not being compatible. Don't see any other reason to not support a dock, it is a shame. I mean it probably can't physically fit into the current dock, but they could always release another dock or an adapter/cable for the current docks. Dropping support for video output isn't going to reduce production costs.
If it can be docked then almost no point in buying the original model anymore since this is way cheaper, more battery life and have better design form factor.