You have a point there Dangerous, but I think its due to price and the changes, or lack there of, through the model years. Especially on the 500's, they stayed the same for a long time, so if you are buying a used bike its about price and condition, not features of the newer models that are the selling points. (until you start talking hybrid ergos)
96 kx250, 97 kx500, 86 kdx 200 (current profile pic)
Hauling seven including Teammate's Hondas, (92 cr500, 02 cr250) and gf's 03 KTM 105, and 99 YZ 125.
They all need complete maintenance. If you go through them and keep up with bushing and bearring wear, and of course engine maintenance, they all are screamers, when they say "Kawasaki" on them.