Play dawn of war 1 and then play dow2. Dow1 used base building perfectly, to make all of the race's play completely different. Necrons used only power, orks needed wahhhggg, imperial guard base were all bunkers you could fire from, Chaos bases were covered in taint that hurt morale, tau could build 2 different buildings to get 2 different tech trees, eldar base could be stealthed and even teleported to different areas, SM were the generic side, dark eldar had buildings that collected souls for extra abilities, and sisters of battle used faith but largely functioned like a generic side.
The point im making is, all of this was thrown out when you dont have bases, and it is too shallow. This is why base building should always be in a RTS.
Well sure:
Command and Conquer Generals:
--Chinese buildings could be mined
--American buildings spawned Rangers upon destruction
--GLA buildings could be left with a "Hole" that would re-build the building
Starcraft:
--Zerg buildings must be built on creep, regenerate health.
--Protoss buildings must be built in power field, regenerate shields
--Terran buildings can lift off, be built anywhere. Can burn down.
That's all well and good for a modern/sci-fi setting, but this is a World War Two game we're talking about here. A field first-aid post set up by the Red Army, Wehrmacht, US Army, British Army, or Imperial Japanese Army isn't going to differ by all that much between factions.
And for a World War Two game, it doesn't make a whole lot of sense to train troops and build tanks on the field of battle itself... defensive options like bunkers, of course, make perfect sense.