Now you may ask "so what?". Well, it opens they door to AH monopolization (i.e. when someone buys all the items in a category and relists at higher prices.)
When the prices were low, he would slowly lose his money, since a lot of products would not be bought, thus AH deposit fee would kick-in. But when the prices are high, that fee (which is based on vendor sell value), can be simply neglected, since those items which will be actually sold, will easily cover the expenses. So the monopolizer will be able to relist his stocks again and again.
Another thing worth mentioning is: current gold sinks, like repairs, food, mounts, deposit fees, training and flying costs are static. They don't change depending on the current buying power of gold. This means that while the amount of in-game gold is relatively low, these sinks will do their task nicely. But once the prices go up, their effectiveness will spiral down at on ever-increasing rate.