actually, that is most certainly how it works on some level Chris, especially with these older titles where the audience is shrinking and unlike modern posters where the audience is increasing. There are curves and valleys as well as peaks. But even for modern posters it happens.
I sold a Mighty Aprhodite DS Doorbell style for $89. in 2008. At that time, I had a few requests and sold others. When I auctioned my next copy however, several had already been sold on ebay & elsewhere and the price kept deteriorating and now it is a $3.00 poster because when there are none around, they go for alot, as more copies get sold in to short a period of time (and that time varies from one title to the next) and the market gets exposed (which usually means more are sold than the market has real buyers) prices either go up or down depending on the title. The next Dracula in the boat 1sh that comes up will not be priced against the $310,000 sale to DeLuca, it will be measured by the $143,000 sale more recently. That doesn't mean it will only be $143k, but it will be used as a measure. That measure devalued to some degree the $310,000 sale. Market affect
Star Wars is immune to devaluation it seems because it has a large, but if 100 copies of a Style-C are sold by auction in 2013, it will also tumble in price because there won't be 1000 people willing to pay top price.
also Chris, if you look at the bid histories, the 2nd & 3rd bidders last time were the 2nd & 3rd bidders this time, both of whom had bid well in excess of $145 last time. so even the likely bidders backed off - that is a bad sign. It means they also lack the confidence in the poster's price.