nVidia did not drop their prices because they do not have to. Sure let the disgruntled gamers go and buy a Radeon HD instead, but even with that happening, nVidia cards are still selling very well.
Can nVidia drop their prices? Sure they can, but dropping the price to attract more buyers can also decrease their revenues as well. nVidia is a for profit company and it will not drop prices unless it needs to.
In a nutshell, nVidia is in a position where it can afford to loose potential buyers looking for a bargain, while AMD is not.