I don't think they meant that Jagex would use the 'player value' to restrict offers on the exchange. Rather, offers on the exchange affect 'player value'. This wouldn't even come close to curbing prices, certainly not directly, in any case. Think of it as an in-game sort of reference for the general going price for an item, for example, if the player value of, say, sharks was identified as 750 gp, somebody could sell them for 1 or 10,000 gp as they wished, the only thing I can see a system like this actually reimposing itself in is the tendency of players not to pay much above the player value. Also, I don't consider myself an economy expert, so feel free to correct me if any of my deductions are incorrect :)