Sometimes, I just wonder why people are so concerned about people selling camera equipment.
Just do a search, and you will find so many threads created asking such questions for the past few years.
I guarantee you that this kind of threads will continue to surface.
By the way, why isn't there a thread on why so many people dumping their EOS 1Ds mk II? The answer is obvious, isn't it?
It is all about demand and supply. How many of us own the 1Ds mk II that will create a huge supplies in the 2nd hand market even if there is a replacement model in the future. It's an expensive camera body ~ $12,000 new.
On the contrary, cameras like EOS 20D or 30D or even the EF 24-105mm f4L are dumping like nobody business. Why is that so? Simply because there is a huge supplies in the 2nd hand market as they are quite affordable. People can simply sell them away due to whatever reasons.
Moreover, buying and selling of gear is part and parcel of a hobby, not just restricted to photography.
At the end of the day, what is your focus? Photography?