Kev, I could definitely do this on less CPU, less RAM, less power, and possibly less money (some of the parts for the custom small atom boards are more expensive, pound-for-pound, than their mainstream desktop counterparts). But the moment I hit any extra task, my spec would be all out of whack and I'd have to rebuild the box. No thanks, I'll accept a higher initial spend and a less-than-optimal running cost as insurance against the time and effort I spend keeping an infrastructure box up and running over that time period.
To give you some math back, my time on salary comes to a net of (approximately) €20/hr (and yes, it'd be far higher if I was contracting, thanks). Lets say a hard drive goes because I bought a different PSU which was closely matched to the spec but it's a friday model so the 12V line was kinda struggling. Now I have to buy the new hard drive, have it shipped, install it and rebuild it; that's going to come to 1-2 hours of my time in total on repairs, and probably three to four days where I don't have my infrastructure here which comes to around 24 hours of my time where I'm being put out because of a hardware failure. That's €480 worth of my time, against about $163/yr in running costs (because I really doubt this will be pulling 250W continously). Think of it as health insurance - yeah, odds are you'll never get back services equal to what you paid for, but that's not really the point...