Just supply and demand. When someone finally manages to bag some unreasonable asking price for a certain lens or camera, everyone holding holding one of those things will suddenly spring into action and put theirs up for sale. What was once "rare" suddenly becomes abundant and the price will drop drastically. Timing is everything. For example, the best time to bid on select field lenses is when everyone into that kind of thing is out in the field, or around Christmas, when people are trying to drum up cash. Or this whole switch to digi. But overall, it's by far the most affordable time in history to acquire film lenses, bodies, and serious darkroom gear. There's simply a glut of good stuff out there. The down side of that fact is that it discourages manufacturers and retailers from getting involved in any new products.
The mantra of the new era is more and more things which go rapidly obsolete and are frequently repurchased, ala consumer electronics.
I prefer to ignore all that stuff.