They didn't mention from where they took the value, but I would assume that they are talking about Open-PvP worlds. As you know, most of Optional-PvP are more likely to have a bigger values for items (kind of a "natural inflation" that we can observe between different worlds with different styles. Money tends to be more valuable on Open-PvP and Enforced PvP, so we can expect the value of the rare items having a higher price on Optional-PvP worlds). Thanks for mentioning this important detail that I overlooked!