I used to sell cameras and video cameras at retail when I was a kid. I was typically the #1 or #2 salesman out of a chain of 13 regional stores every month. I have sold cameras to many, many people. I helped people select the right camera setups back in the days when there were Nikon, Canon, and Minolta AF SLR's competing for the higher end, and Olympus, Pentax, and Nikon all competing fiercely in the 28-90 or 28-105 type all-in-one zoom camera segment. Although the time was different, the retail camera buyer still has the same basic constraints and concerns: brand awareness/prejudices/opinions/habit, budget, system-locked-in or not?, personal preference, size, and weight, status, social pressures.
Buying the right camera is a personal issue. I dunno...there are a lot of different reasons people buy a camera. The camera companies try very hard to create the desire for people to buy NEW!! NEW! stuff. At times, the product matrix develops a new wrinkle, and suddenly people feel that they "need" a new set-up, for whatever reason.
Right now, we have a lot of good cameras in a fairly mature market, but if somebody has say a D70, but that small child is now a high-school sports player, buying a MUCH-newer, better at High ISO camera, or a new fast-aperture lens, can make a world of difference in poor lighting.
The D7100 and D7200 are very mature, very fancy cameras. I would trade a 10-years-old D2x or a D70 for a D7200 in a second.