Collect resources. Build up your base. Climb the tech tree. Collect more resources. Pump out a ton of upgraded units and overwhelm the AI with an unstoppable army. Rinse, repeat, and you've got yourself a single-player campaign. That's the way Dune II did it back in 1992. That's the way StarCraft did it in 1998. And that's the way the original Warhammer 40,000: Dawn of War did it in 2004.
The formula seems to have worked pretty well so far. But Relic Entertainment isn't interested in kowtowing to tradition with Warhammer 40,000: Dawn of War II. It's amputated everything it found tiresome about the RTS genre with a bloody chain saw sword, focusing on what it loves with the fine precision of an Eldar splinter rifle.