Interesting idea. That might very well be how it works.
However, it goes against both how the regular Exchange works, which would influence how the zen sellers would price their zen. In the Exchange, if you want your thing to sell quick - indeed, often at all - you want to make your price the lowest, so people will want to buy it, because it is at the top of the first page. It would only make sense that the Zen Exchange would work the same way - the stuff that is the lowest price would sell first, since folks want to get the most zen for their dil.
If it works like you say, any schmo could artificially drive up the mean price of zen - you just put a high-ball offer up, then it knocks the lowest price off the screen, making the next lowest price the lowest, etc. It screws all the people selling low, not just all the folks that were selling for the former lowest price, but also everyone who thinks the Dil exchange works like the EC Exchange and are low-balling the price in hopes of selling their zen faster.
I guess that could be tested...
See my edited post - its too hard to think straight right now but it is right - not saying that Cyptic is not supporting the price - but you are looking at this backward - confusing dilth with Zen in your reasoning.