Being from the UK, I can comment on this. The issue we have over here is the lack of numbers of cabs to buy. Missile Commands, Robotrons, Pac-Mans - the classics basically, simply don't turn up, and when they do, they go for well over £1,000 for the most part. To give you an idea, an Irish Asteroids Deluxe upright in tatty shape and non-working condition sold on ebay UK over the weekend for £720 (which at current exchange rates is $931).
http://www.ebay.co.uk/itm/Asteroids-Deluxe-Arcade-Machine-/192180648011
This is the market we are in over here. And to your point, you are correct, I can't imagine a non-working Asteroids Deluxe going for $931 over in the USA.
There is a regular container that comes over here from CoinOpWarehouse every couple of months or so - it gives collectors an opportunity to acquire a classic cab at a reasonable cost - to us anyway.
It's market forces, pure and simple. Supply/demand has driven prices up over here. Add to that the lack of good titles to buy - hence people are importing from the US, and are prepared to pay what you guys see as premium prices. To us, the prices are resonable to acquire the titles we want.
As for buying from a single picture - part of the thrill is buying a project that needs work. All part of the hobby, and there's an acceptance that most cabs bought from the US will need work of some sort.
I've yet to get in on the US import action, but I can see the appeal.