Maybe this is the case for US coins, but not mine. Mine have been going up steadily for a decade, but accellerating the last couple of years. To me the US market has always been a unusual one, with sky high values for items labeled "key" but are still relatively common for any other country.
Chris ancients and their market are an entirely different animal and you really can't compare them to US coins, or even world coins for that matter. But yeah, I do understand your point. Back in '02 I quite collecting US coins because I knew they were going to get too expensive to buy. I switched over to collecting world coins because they were a bargain, I liked the designs more, they had more history, and greater rarity. By '03 or '04 I predicted that world coins would start to see a run up in values because more and more people were starting to do the same thing I was doing and for the same reasons. And yes, it happened. But the increases for world coins lagged several years behind those for the US coins. So my thought is that the same thing will happen in the world coins market that happened in the US coins market - there will be a correction. I think it's just a matter of when. Time will tell.