plenty of single rail 800-1000W psu's are around, and they are better in general.
about 99% of "dual rail" or more psu's aren't actually dual rail, they simply split the initial voltages across different leads to meet a pretty ridiculous safety standard, thats even ignored anyway on most of the higher multiple rail psu's.
i think it was intel that pushed forward the safety spec that you shouldn't have more than 18amp's down any wires. so after the 12vrail is all nicely made you simply have overvoltage protection that stops more than 18amps going down any specific cable. which is fine, but some things, possibly an very very overclocked cpu, or a gfx card can need more than 18amps. often now we get 3-4 rails in the psu's aimed at people with quad cores and 8800/2900's so the cpu and pci-e might get their own cable. but a dual rail psu will often have say all the pci-e on one rail + say, molex's, on one single rail, and mobo connector and atx2 connector on the other, which can feed a lot of juice to pci-e slots and quad cores and can limit overclocks if you can't break the 18amp limit.
after what, 1-2 years of this , basically, completely useless standard even intel gave up on recommending them. a heck of a lot of the multiple rail psu's now let you use 20-24amps on a rail anyway, which means those psu's are multiple rail for marketing reasons only, and could still screw you on the power you need and where you need it. a good single rail psu still has the usual voltage/current protection and are fine, but mean you simply don't have to worry at all about what you've got connected to what rail.
1000w psu's, for home users, in general are complete overkill. but you really do generally want a 500W for an overclocked 2900/8800 dual/quad core setup. you really do want to be going up to around the 750W area for sli/crossfire on those. what about if you've overclocked even further, have 8 drives and a soundcard, bunch of powerful fans, a 1000W psu isn't the worst idea ever. but very few people need them, remember you're only gonna be loading the 2 gfx cards IN a game, you're unlikely to be transfering data across all the 8 drives at the same time, or loading all usb/firewire ports at the same time and burning 2 dvd's.
but then again, a few people do have dual ath fx setups(few and far between) and those with crossfire will take a heck of a lot of power.
what about a server setup with 8 sticks of mem and 2 quad cores and 15k raid.
then, we've just seen a quad core barcelona setup being demo'd with 2 2900xt's, and a 3rd 2900/2600 card doing physics, so thats more power beyond the 750W for crossfire. the 790 chipset is set to support quad crossfire, in which case i would think you're looking at 1000W psu not being enough.
cpu parts get cheaper to make, they start off expensive, then yields increase, tech moves forward. tech's kinda dead on PSU's, the parts inside don't change massively, they are rated for pretty high temps, and you need good materials to not fall apart at high temps. you're also paying for the warranty aswell, which, has in general been increased over the past few years, while the usage and load on the psu's has gone up, which would likely cause increase in failure rate. much heavier than really anything else, so higher shipping costs add in there a little. i mean, a computer case, theres no real tech, its pressed metal mostly, why are there incredible expensive cases that use fairly similar quantities of metal to cheap cases.
