I might be able to help with this. You see, in Wow things like ores and herbs are actually very common and avaliable in limitless supply, but only some players have real access to them. This means that these substances are highly controlled. For example I once had enough herbs in my bank to destroy the entire herbalism industry if I put them up for aution all at once. If a player needs some of these, especially those that advance a proffession or at the end of a long quest its annoying to have to pay for goods that are usually only ever 5 feet away and are unlimited.
However, unlike real life a player doesn't need this stuff to live so they could just wait for it to get some competition and the price to come down. A game world manages to avoid those nasty aftereffects of open capitalism. So in the end it comes down to players being annoyed that the last roadblock between them and success is one that they generally can't surmound by their own skills and they relly on the generosity/mercy of others to get though.
