Other components do require some power, but they are minimal.
Almost every pc will need power for a cpu, ram, dvd-burner, fans, and a couple of hard drives. It is a given for any general recommendation. The total does not amount to enough to make much of a difference. If you have a case full of hard drives, then it starts to make a difference. What DOES make a big difference is a high powered graphics system. A higher powered card like the 4870 or GTX280 will need a second pci-e connector that can deliver 75 watts. If that card is duplicated for SLI or crossfire, then that is a BIG jump. For those deranged souls who try tri or quad sli/crossfire, then you need a really capable psu.