I think you would be very surprised how many 5DII owners have 7Ds as well.
The cost of the 5DII is not just the body - but the lens as well. I have a 400f/2.8 IS which is a terrific super tele on the 7D. What lens for the 5DII would you suggest would match that?
Take my 70-200 f/2.8 - on the 5DII the nearest is the 70-300L - not really a match.
Move down to the 135F2 and 85 f1.2 and do the same comparison.
The 5D2 is a great camera - providing you can get the lens, the fps and the AF to match the subjects you take.
The 7D is the top of the NON specialist bodies.
Not quite that simple -- if I do the same comparison for the 135 and the 85, the 135mm f/2 replaces the 85mm f/1.2 on full frame (at about half the price) and the 200mm f/2.8 replaces the 135mm f/2. On full frame, lenses like the 85mm f/1.2, f/2.8 zooms, and the 200mm f/2 have no replacement on APS-C that provides the same dof and fov. So if you want shallow dof, you are much better off with FF.
In terms of the 400mm f/2.8 -- you have the 600mm f/4 which is about the same weight.
You will generally get more reach for less $ on APS-C though (you also have access to several very good and inexpensive wide angle choices)