That review is bullshit. It's not going to tax your machine, but that's a good thing. The unit type thing is also missing that not the entire game takes place on the battlefield, there's multiple layers to it and you almost never win through pure domination.
EDIT: Also, ground vehicles? This is Dune, you can't cross sand in a vehicle, and they couldn't go up cliffs. No, instead you airdrop, which is way more flexible.
John Carmack, author of the Doom engine, is a long time Linux user and for a while the policy was to open source the idTech engines once they had moved on.
However, Doom was hugely popular on its own before this, and was actually more pivotal for making Windows a gaming platform (over DOS).
The reason it runs everywhere is a combination of it's huge popularity, it's (now) open source and it's generally low system requirements.