1. Stardock anticipated the release of Sins on Steam to cannibalize their direct sales through the Stardock store and Impulse. They expected Steam sales to share the same digital "pie" that their own sales and Impulse shared.
2. Instead, Stardock found that their direct digital sales and Impulse sales were largely the same. This one's a bit ambiguous in their announcement.
3. Their Sins Steam sales eclipsed their retail sales.
4. (And most importantly!!) As a result, Stardock plans to bring Elemental and The Political Machine to Steam.
I've always wanted to try Elemental, not that Steam really factors into this decision. I'm more inclined to support Stardock directly by buying direct from them. That said, seeing more sales through Steam only means good things for Stardock and hopefully that translates to more resources into better games. Elemental's initial release was marred by issues.