It's really not, actually. I got a $699 desktop, and I could run any of my games without lag on the highest graphics. It was their cheapest and smallest computer.
You didn't post specs so you didn't prove anything.
Here are some reasons people say alienware is overpriced:
1. A custom built computer will ALWAYS be cheaper for the same specs guaranteed
2. There are other sites that prebuild computers that will do it cheaper also for the same specs
3. Like most prebuilt computer companies they always give you 50 gigs of ram and a quad core billion ghz processor and then give you a $100 GPU(the most important thing for gaming)
4. They are