Ten years is a long time... long enough for markets to get turned upside down.  Seriously, I wouldn't be surprised if a new competitor wipes both Steam and Impulse off the map over that time period. It's just a long time.

In any case, I'd compare this to the Sega/Nintendo console bickering I saw in my elementary school days.  Sure, Sega could have gotten a few extra sales by releasing a Sonic game on Nintendo's system, but that would be strategic suicide.  Sonic was the reason kids were buying into Sega's platform.  It took the complete annihilation of Sega as a platform to see Sonic on a Nintendo console.  Unless Impulse goes under, we won't see them releasing their exclusives on a competitor's platform.

My bet is on Armageddon. And hell is a real place, but won't freeze over (it's just too hot!).

Stranger things have happened. Seriously though, if you want Sins, just get it retail or through Impulse. I have no love of Steam but I enjoyed Left 4 Dead to pick it up on the cheap. You've already let them know of your opinion, so no sense in keep asking. It's not as if Valve games are the only games missing from Impulse anyway.

You obviously know nothing about exclusive content.

Also, Stardock isn't a normal company. Brad 'Frogboy' Wardell (thier CEO) doesn't make decisions based on the bottemline right now, he makes them based on what will be better in the future. And building you own digital store using exclusive titles so that one day it will compete with Steam is far better in the future, even if costs them some sales now.