Steve, you might be confusing popularity with competency. Nikon mid level cameras have not taken the performance backseat to Canon or Sony for a long time(never to Sony). What Nikon camera is a lesser phototaking machine than a 7D? Sure the Canon has a lot of features and for some customers that means an advantage but surely you have compared images with your Nikon's and 7D and 5mkII. Any way you slice it, the low ISO noise and blotchy banding ruins a lot of images that are keepers under the same conditions with D40 through D3x. I had a slight feeling of envy of my friends shooting 7D and 5mlII in the same events or clubs until I got a chance to see prints and full screen images on decent monitors instead of the camera back LCD's. My D90 had cleaner skies, solid color backgrounds shadows than either. When I got the D7000 the tradition of just better basic image related performance continued. Here is a video done by a respected reviewer using good technique. His blog has a lot of carefully done tests that are revealing. His examples show clearly what I was even with the D90. http://testcams.com/...blog/2011/05/03/nikon-dx-vs-canon-aps-c-dynamic-range/ Currently Canon has no camera camera under $3500 which is as clean and free of artifacts as the D90. 5100, 7000, 300, 700, 3 or 3x.
As far as the Sony machines go, each time they release the next Nikon beater the luster and excitement quickly fades when the reality does not quite match the promises. Do you know ANY serious photographer who has moved from either Canon or Nikon to the Sony system? The initial test photos of the a77 underwhelmed even the Sony fans with visible noise at ISO 200 and mushy images.