It's normal fluctuation of the market. With the amount of gold in the game ever-increasing, inflation is inevitable.

With regards to prices changing, this happens every new cap. The items are initially worth a lot and people who can afford pay high price, low supply and high demand. As demand at that price falls, so does the price until it reaches a new equilibrium. This will happen until the price stablilizes at a low point.

With respect to other items, when people need cash to buy the new expensive gear, they begin to sell their other stuff. With many people doing this the prices will fall. The longer the cap is out, this trend will reverse. People stop buying end game gear and invest in other items, thus the demand becomes higher than the supply again and prices go up.

This up and down fluctuation has happened for a while, and will continue to happen with each new lelevel cap.