It's also called value-based pricing [1]. You're correct in your edit, hotels/airline tickets where you're auctioning off a limited value is one thing, selling a inexhaustible commodity at different rates without any reasonable factor like location (water in a desert = more valuable) just feels dishonest.

Amazon and Travelocity rightfully caught a lot of flack when they were caught trying this (perhaps pricing A/B test?) years ago.

[1] http://en.wikipedia.org/wiki/Value-based_pricing