Glen: the D2H is not a general-purpose dSLR; it was designed specifically to meet the needs of professional photojournalists and sports photographers. I assume it will meet their needs admirably. For them more than 4 megapixels would actually be a liability. They need ruggedness, autofocus, low light sensitivity, and above all the ability to take many pictures in succession. The D2H is the direct successor of the Nikon D1H and the direct competitor of the Canon 1D (not the Canon 1Ds).
Everyone will be asking why Nikon didn't release a high-megapixel 1Ds competitor. From what I've read Nikon has had profitability problems and is concentrating their R&D on those products which will put them back in the black - primarily low end compact digitals. A 10 mp or more D2 would be a nice showpiece but wouldn't sell in such volume as to affect the bottom line. Many people assume that the laws of economics dictate that Nikon and Canon must perpetually duke it out in the extreme pro camera arena, but the marketplace says otherwise. If I'm not mistaken, neither Nikon nor Canon are currently raking in the most profits and volume in the digital camera market. I believe that title goes to Sony ... and Sony doesn't even have a dSLR, let alone a pro dSLR.
There are several signs that the era of ever-increasing megapixels may be coming to a close. Norman Koren, who has an excellent technical grasp of digital, suggests that 4 or 5 megapixels is not only sufficient for consumers' needs in a compact camera but is about as many as can be squeezed out of the tiny imager form factor these cameras employ. Similarly, 6 megapixels is a sweet point for dSLRs both because of imager cost and because most 35mm SLR lenses demonstrate aberration problems and perhaps insufficient resolution to justify more megapixels. 6 megapixels is also more than enough for on-line presentation and printing up to 8x10, which is all the vast majority of photographers ever do.
Nothing precludes Nikon from eventually producing a 10 mp or greater dSLR, but it's quite possible that Fuji or Kodak will get there first - although not likely with a pro body.