i haven't heard about this 'Steamworks' before so i shall hold my judgement for now. my first impression, though, was that it's a engine wise thing which would require an entire recoding of the already complete engine. that said it could just be a compatibility front-end to patch in Steam with the game in question.
As I understand it, it's the latter, but I'm not completely sure. I'm just saying Steam/Valve have provided a tool for ensuring a new game is compatible with steam- whether game developers choose to use it is up to them - Valve can't recode Steam everytime a new game comes out.
That said, I can understand Stardock not being too worried about Steam compatibility, now that they have launched Impulse. Personally, I'd love it if Demigod supported the steam overlay, as that's how I talk to my gaming friends, and I don't need to tab out of the game to chat with them.