It is called market segmentation, a basic marketing strategy to target specific markets with a marketing program - of which price is one factor. Most successful companies do it.
Alienware is selling their brand. If people want to rely on their high end brand instead of doing research for themselves - including alternative prices - then they are chosing that option.
Competition, when it happens, will keep prices down, but consumers have to play their role in competition and compare products and prices for it to work. If they choose not to and just pay a higher price, that is their price for not fulfilling that role. Course the more profit companies make off the high margin business, the less they have to make on the low margin business. So the price conscious buyer is doubly rewarded for his efforts.
It is a great system - when you don't have monopolies, oligopolies or monopolistic competition - for bringing order to the the production and distrubution of goods and the allocation of productive resources and for fostering efficiency and innovation. However it leaves a lot to be desired with respect to the allocation of the profits and wages of production.