According to the military that I used to work with, gold is expensive not because of how rare it is, but because the U.S. government buys it up and trades it to countries we have a debt with. It is one of the few currencies they accept as payment. This is why all these "cash for gold" businesses cropped up.
As far as the 15 dollar price tag on armor, it is plain stupid. If you buy it, you really need to learn the real value of a dollar. Even if you are rich, it is a very irresponsible use of money. Unfortunately when people feel like they have a surplus of funds, it becomes real easy to let go of it for frivolous things. Therefore Bioware gets away with it.
Even at $5.00, I would have worked pretty hard for 15 minutes for it at my job just to get pixels that really don't do anything but make my character pretty. What I do during that 40-50 hours a week seems way more important to me than a set of game armor, therefor no silly spending for me.