Darwin: No matter than a smidge of perfect gems to that niche buyer out there who's actually interested. By default, that makes plain ones all but worthless as all.
angeldesignpro: Handful of gems at most. Very limited usefulness, once again.
LiquidClear: A lot to the right person if it gets two sockets. Virtually useless with just one socket. That's vague and slightly overblown, but the sockets really do make a huge difference.
THC: I agree in principle, Greebo is more or less right. Numbers and logic don't often take part in determining trade values. Someone out there made such a trade in the past, and people thereafter simply followed along, creating a trend. It doesn't have to actually make sense.