From what I've seen in the last couple years...this 'unlimited' market is actually growing way more than people getting out (At least in the States).  I've been collecting since about 1998 and I've met more new collectors in the past 2-3 year...than in the previous 10. I know of a local guy that started collecting in June.  He's an arcade game collector and wanted a pin.  I sold him my Sorcerer for $500 to get him started.  He now has well over 10 pins (in less than 3 months) including a NIB Stern and a couple HUO Sterns.  I don't know of a single person that's gotten out of collecting.

Simple supply and demand.

I will give you the perspective of the otherside. I am new - the pinball wax behind my ears hasn't even dried yet.  I am I have been a PC nut for a long time - however held a very solid intrest in playing pinnies - not owning them.  I have just recently taken my first step into the market.  I can say that after my purchase I know of another 3 other mates that are now seriously considering making the jump.  Specially with the recent Mancave explosion.  I recently finished making a mame arcade http://clints.weebly.com/arcade.html - but after buying this pinball I am damn hooked and have been throwing myself into it.

I think this graph regarding pinball sales says a lot - http://www.bostonpinball.biz/ebay0512.htm and confirms what Monster Bash is saying - sales dropping with prices rising.  The problem with pinball is that there are only so many machines out there - with very few machines entering the market.