I can throw my Internet connection router and FTTC box on as discretionary load but that's another ~300Wh/day; it is quite staggering how relatively efficient the RPi is, compared to presumably similar or lower processing requirements in the other two boxes!
http://www.earth.org.uk/off-grid-stats.html
(You can only see the RPi's power consumption when the networking gear is pushed back onto mains.)
I thought the article was very clear about that as it's point. If you were thinking of using an RPi as a server, it's not meant for that, here is a better alternative.
Ubuntu and some of the other 3rd-party OSes are compiled for ARMv7, and won't run on the 0/1/1+. A couple are compiled for ARMv8/AARCH64, and won't run on anything but a Pi3. There's a lot of work that went into making things like Raspbian as close to foolproof as possible.
2. It is tiny
3. It is quite power efficient
4. It has GPIO pins, which make it usable for experimenting with hardware.
5. It has a great community (you can easily find many projects for it, and there are some great OSes available, which run nice educational software)
6. It is cheap
All of this makes it fantastic for education and as a gadget. The whole point of the raspberry pi is to be unlike other computers. You can set it up as a server, but this is not its main purpose.
The Dell Optiflex FX160 probably outperforms the pi at all measures, but it is just stupid to compare it to a raspberry pi, because it has none of its unique points which make the pi a good choice in the first place.
Now, there are actually some better raspberry pi clones out there. For those products, a title like this might make sense.