These 1000W PSUs are a case of convincing people they need something they don't. There is a lot more profit in selling a high-end PSU than in selling a 400W PSU. Few people need a 1000W PSU. Most PC enthusiasts don't need anything over a quality 500W PSU. If you purchase a quality PSU it delivers both the quantity and quality of current you need and maintains tight voltages. Many PSUs are over-rated and don't deliver the power they claim and the voltage regulation is poor.
GPUs will soon consume lower unit power as they have a die shrink to 65 nano but as long as PC enthusiasts will pay for more transistors, that's what graphics chip companies will produce, even if the increase in performance is pretty insignificant compared to the increased power consumption. Some people are willing to pay two to three times the price of a CPU for a graphics card or multiple cards. This results in huge profits. The PSU folks see an opportunity to jump on the band wagon and they are, so you can expect them to tell ya you need a 1000W PSU.