On the other hand, you can't automatically assume they don't care about it at all.
I build most of my desktops, and I certainly want to reduce power usage when I'm not using them. Enough so that I'd pay for a power supply that supports the lower power states.
Not everybody who builds their own PC is doing so to make a ridiculously over powered system.
I agree. It really depends on why someone is building the PC. Sometimes you want to optimize the gaming performance, or video editing performance, or the file transfer speed and lower latency for a NAS box, or other times you're looking to optimize video playback, low power consumption, and low noise on an HTPC. All of those could be built by ones self, and each will usually require certain choices and trade-offs to achieve the desired goals.
I build most of my desktops, and I certainly want to reduce power usage when I'm not using them. Enough so that I'd pay for a power supply that supports the lower power states.
Not everybody who builds their own PC is doing so to make a ridiculously over powered system.