Let's face it, price is not the only parameter that determines what Nikon calls a "pro" camera. If that were true, then there would only be ONE "pro" camera [the most expensive].Let's face it, the 610/750/810 are all semi pro cameras--each one exhibiting some pro features. However, none of them are even close to the flagship, professional d4. Thus, it costs 2-3x as much.This is simply DPR's opinion. If you look at Nikon's list or "pro" cameras, the D810 is on it.It's funny that the 800/810 has a pro build and yet their not even considered pro cameras. As dpreview suggests, Nikon has three "semi pro cameras" -- the 610, 750, and 810. They really should match the semi pro 810 with the appropriate, corresponding semi pro body.D750 is NOT built as good as D300 was.
D300= D800/810 build wise
D750= D7000/7100/600/610
D300 was built tough as a pro body should
Not saying D750 is cheap or flimsy at all but D300/D700/D800 series is just notch above. It is obvious the moment you pick up the cameras side by side...
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http://www.pbase.com/jps1979/galleries
nikonpro.com lists 18 cameras that qualify for NPS membership:

The qualifying cameras for NPS membership...
It doesn't matter what DPR thinks. It doesn't matter what you think. The above is THE LIST.