I know all companies are out to make money and having to buy all new accessories every time you update your camera can generate a lot of cash. But I would not be surprised if a lot of people put off upgrading simply because of the cost of buying all new equipment.
For example the grip on the 7000 will not fit if you want to upgrade to the 7100 yet both cameras are virtually the same size. So not only do you have to pay 1200 for a new camera but 300 or so more for a new grip.
If the same flash can work across the entire Nikon line I do not see why they could not come up with a remote that will work across the entire line or at least offer adapters or converters that you can get to connect different accessories to different cameras.
A lot of third parties make a lot of money offering these accessories and while I may want Nikon Cameras and Nikon lenses I do not see paying $400 when I can get a functional grip for less than $100. Even if they only last a year I can get 3 new ones before it costs as much as the Nikon.