I have my RPi B+ running all my Internet facing services and running off-grid in gloomy London at under 2W, nearer 1.5W when I can fix some transient issues.
And if I need something lower power I have Arduino-like boards that I run on microwatts, eg for battery-powered remote sensing.
I see all the complaining about memory and speed but as someone who grew up with a Z80- and 6502- based set of home computers, then used Sun Workstations with a few MB of RAM and tens of MHz clock, the Arduino/ATMega328P matches the Z80/6502s in performance at a millionth the power and has non-volatile storage built in, and the RPis are and order or two of magnitude better than the workstations and a couple of orders of magnitude cheaper.
I can fit almost all that I need to run with careful use of resources into the RPi/Arduino world and still have lots of elbowroom left over.
Yes, I've worked on big systems for (eg) big banks, but most of us really need GHz and GB on every machine? Some yes (like my MacBook), but most no.