Originally Posted by myself, kinda, in a pm

It is correct that markets determine price through evaluation of both demand and supply. The part that is often forgotten is that each side operates independently of the other. The number of quality drops out there only affects the supply end; it doesn't change demand at all. When examining demand, we look at the aspects of goods that make them appealing (or not, given the situation). In terms of GW, there are really only two variables here: stats and appearance. For some players, a collector longsword is just as good as a crystalline; others place a high value upon aesthetics and choose to bid up prices for more unusual skins.

The biggest reason that prices drop over time is that GW goods don't follow the same rules that real-life ones do. Pixilated swords never rust; my ranger’s bows don't break. Once an item is created, it will not degrade or disappear unless a player does so intentionally. Even the rarest of items becomes much less so in the long run simply because there is nowhere for it to go, barring customization/dedication. The only exception would be something that is available for a finite short-run timeframe, such as the new polar bear mini. An item like that presumably has an unchanging, vertical supply.

Nightfall also had an immense impact upon the weapon market. In essence, the advent of inscriptions increased aggregate supply to levels we had not previously seen. The ability to pick and choose an item's mods, combined with easier salvage, made “perfect” weapons more common than ever, and consequently prices declined even further.

Inflation is a term often tossed into conversation, but infrequently in the correct manner. In a physical economy, inflation is neither necessarily bad nor good. On the other hand, a system with self-imposed limitations upon trade (i.e. a game) can confront issues with large waves in a money supply. Ideally, we would not have a hard currency cap, eliminating the need to use ecto or armbraces as a means of exchange. Data storage parameters, unfortunately, do not allow such an environment to exist. As mentioned above, virtual goods have a tendency to accumulate over time because they are superdurable. This leads to an ingame wealth creep in which everyone from typical Joe Warrior to the dedicated Miss UW Monk has more platinum lying around. To counteract this inflationary effect, we must either remove wealth from the economy more rapidly or alternatively slow its rate of entry. ANet has done both in the form of titles and loot scaling. By creating additional goldsinks and restricting the number of merchant trash pieces that players receive, the population as a whole has less currency on hand and price levels are held in check.

You might notice a pattern: nearly everything about GW's design eventually drives prices for weapons and minipets downward. Dyes, runes, and crafting materials function differently, in a manner that more closely resembles real-world goods. They exist to be consumed and as a result are subject to normal price fluctuation and cycling.