Quoted from dos_reboot:

Reposted from another thread (with new format)...
When I started collecting (before prices really climbed), it seems that more collectors were willing to rotate their titles more freely with the understanding that if they ever wanted that pin again that it would be easy and cheap enough to find another one. Games were cheap and plentiful. Not in the best shape, but if you wanted a certain pin they were out there for a decent price. Even NIB were somewhat affordable.
Economy tanked. When Stern had to increase prices to stay in business it seemed the sky was falling. Collectors started hoarding games thinking *end of pinball times*. Once games were harder to come by, collector started to lock in their 'must haves'. This drought drove up prices even more which in turn tighted collectors grips even more ("I can't let go of my <insert A-title here>, I'll never find another one for <2005 price> again in 2010".) Grail games were restored, increasing their investment.
The economy came back. Pinball came back. Pinball grew in popularity. Seeing prices hadn't retreated, collectors continued to dig in their heels and refused to sell. This created a somewhat false demand in games for the few who wanted certain titles that were sitting idle in many collector's basements. When they did sell, restored games fetch crazy prices. Stern/JJP's prices and 'tiered' selling model start to reflect the new pin economy. HUO game prices followed. Some LE's become unobtainium further justifying Stern's tiered model strategy. Collectors started customizing on a grand scale, pouring money into game cosmetics. Secondary market prices went up further.
Boutique and remakes see opportunity - some collectors start to 'cash out' with talk of bubble. Prices on some hot titles plateau for first time. Stern contiues to 'push' titles into market, code unfinished/unpolished. Many LE's NIB sit unsold. Market is saturated. Stern/JJP/Boutiques respond by giving collectors what they want - title, designer, features ... even re-running previous titles. Collectors respond by starting to rotate their titles more freely wanting the latest/greatest. HUO games drop slightly in price as result. That brings us to today.
Just a quick take/observation. Feel free to edit.