Having Jagex set the pricecs would create an even worse situation. Instead of bought out items going up over time and the GE price and the street price meeting at an equilibrium, they would stay bought out forever and whomever owned the majority of the items could charge you whatever they wanted. You would be right if the runescape economy were the real world economy (just think of anything involving oil in the last few years), but in runescape with the prices/trade limits, the people who do control a large amount of whatever item, have no more control over the price then someone with just one. I wouldn't like if the economy were at a fixed price though, because it has made me a little bit of income just because of inflation and selling at the right time.