It's a little more complicated than that. There's a complex formula of TDP, die size, RAM cost, RAM procurability, Kinect BOM cost and retail price at work here.
Even if you take into consideration the reduced Kinect BOM costs, the thing is still making the system more expensive for the consumer than it would have otherwise been. Quite more expensive if we go by the rumor that the new Kinect is costing Microsoft almost as much as the Xbone itself.