The high end rewards are so rare that immediate effects on the economy would be negligible. If you check the 180 day graph of some of the rarer items that can be won, prices have either been plummeting since November, or have a nice little sine wave. The only way the update could have had a large effect is if people panicked and influenced more people to panic and then everyone panics. I agree that it is against the spirit of the game, earning things and achievement, and it does open the window to allow Jagex to do more things that can have an adverse effect on the economy, such as directly buying coins and items. However, one must always remember, Jagex is a business that wants to make money. If people want to throw money at them, why stop? Valve does the same exact thing, selling keys to open random crates for a rare chance to get a special hat, and they're pretty successful.