Georg,
Basically, the price is what people are willing to pay. Usually there's a significant drop in perceived value, proportional to how 'old' the equipment is. I can't help but think of the 9600 for sale for $300 in the used equipment section of the site. It was originally $5000 or so....
This is somewhat unrelated, but since we're in the pro business section, it's worth mentioning the importance of recouping your investment in equipment ASAP when it come to digital photography. Gear becomes outdated rapidly, and if you don't recoup and make a profit, you eventually lose money. It wasnt' the case with film gear. Cameras could be used 'forever' back then. This is one of the major changes in the photography business brought by digital photography.
It doesn't apply to all equipment. I bought a computerized mat cutter in 1999, and I still use it to this day. It's operated by a computer running windows 98. But then a mat is a mat. There hasn't been any changes, just updates to newer operating systems. I couldn't do more with it if I ran the latest OS.
So it's not accross the board, and it also depends on your exact involvement in the industry. In advertising, some clients may request the use of specicic cameras or equipment for example. In fine art, it's largely left to the photographer, which gives us a lot more freedom. When the purpose is expressive rather than documentary, which camera is used is less important than what is said. The message, in other words, comes first.
And of course, if you listen to the manufacturers, you must update immediately and constantly. But then, that's how they make their living so it is no surprise that they hold this position. It just gets to be funny when we are told we need ever more resolution. What most of us need is a more well-defined vision for our work, but that doesn't sell as well because it's a lot more elusive to measure.
