Several reasons, but please, this is how
I think, not universal truths (matter of fact I seem to be the odd one):
Basically I don't like giving more than a grand on a body, I STILL think photography is about lenses... this is the MOST important! I don't care, for instance, giving half-a-grand on a Sigma 8mm/4 which I RARELY use. But I don't like giving more than that on a body. I have been shooting (D)SLR since 2000 and I have changed bodies SEVERAL times, but very few times I have traded lenses. Lenses are a LONG TIME WORTHY INVESTMENT, bodies come and go.
Other reasons are:
1- The same reason I used to shoot on a F80s and not on a F100. F80s were cheaper and more modern.
2- D200 battery life is disappointing, and I had a better sync with it with the D50.
3- Along with the body difference one need to count housing body price difference, I am a heavy Sea&Sea user.
4- D80 is newer than D200, better chance of selling it next year if I need it. My friends that bought a D200 here are having a hard time trying to sell it already.
These are the ones I quickly remember, I have reached 3rd place in the Brazillian National UWPhoto Championship with a N80 vs people with F100s and F5s. I have shot extensively both underwater and above, and VERY FEW times I have felt limited by my camera. But OH GOD how I miss a good glass sometimes... like a better and faster tele, or that REAL wide fast lens.
I am sure the D80 will be the BEST CAMERA I WILL EVER HAD until now. For UWPhoto I am much more fond of the DX 1.5 factor now than before, specially after the ESPECTACULAR 10.5mm/2.8 AF-S Fisheye. But for natural photo (my other passion) I still miss something like a Full-Framed D80.
Check my Flickr site, you will see pictures taken with "cheap" bodies, and "no-so-cheap" lenses. Any defects are because of the body and brains of the photographer!
If you need advice about lens I could tell you what I think of a good quiver.
Remember as an SLR shooter you should be buying lenses and accessories forever!!! These are long term investments!
How many times we see WONDERFUL pictures taken with pin-hole caneras? Where is the magic of Cartier-Bresson, on his Leica body, or his Leica Lenses and his photographic view? What about Galen Rowell, no filter on one 20mm on a manual very very light body, so he could climb faster? I had a teacher who used to say: "Your best sensor is your eyes, your main control device is your feet!"
Cameras are nothing but a black box, I used to say that "
f16@1/250s" used to be the same on a F60 or a F5. Nowadays there is a small difference due to different sensors and firmware, but still is about the same on a D40 or a D200.
The magic of photography is performed by the adventurer mind in a world of glasses.