Just registered to add my humble opinion about Stardock/Steam idea.
I am a Steam user first of all. Though when it was first released, i was one of the most passionate Steam haters available those days

. Years passed and we have a much more refined Steam, so much infact i began to LOVE Steam. It's silly to actually love a piece of software i know, but i think it deserves it.
Biggest advantage of Steam is, there are lots of games available in it. Recently i started to repurchase some of my already retail owned games from Steam. Sometimes just for the sake of having it on steam, sometimes because i lost/scratched the disc. But mostly in all circumstances, i was a happy customer.
Still there are lots of people that have problems with Steam, but when you look at the big picture (15 million people using it), you'll see that people that are having problems are a very small percentage of all Steam users. Some people will always have problems with a specific software, if the product is still supported (Steam obviously is) usually these problems gets fixed after some time. Also, dont forget most of the problems are caused by the DEVELOPERS themselves, not by Steam, and it is developers responsibility to fix them.
Better or worse, there are lots of games available at steam. Valve's products are best in my opinion. Some people says Orange Box is not a fair deal as most people agrees. Perhaps from their own point of view it isnt. For the fans of FPS genre, i think there is no better deal currently available. If you dont care much about the genre itself however, its your own perspective. I for one choose quality over quantity, hence why i am so careful about picking my games.
I've been hearing about Gal Civ and more recently Sins for years, but never had the opportunity to try it out properly. With the recent release of Sins i was honestly waiting for Steam release to pick it up. I've been wondering why they havent made their products available from Steam for sometime. Until i started to actually search for the means to buy Sins digitally, i never ever heard about SDC or anything close to it. Though i'm sure people NEVER had any problems with it (not the software bugs but the reliability and trust as a distribution platform) but i'm still concerned about it. Mainly because i have so much games on Steam now, i really dont want a seperate software for Stardocks game.
Most of the people said Stardock doesnt use Steam because steam includes DRM. Yes its true Steam does use DRM for its games but as far as i know, only if developers wants to use it. Developers use it because most of them are paranoid about copy protection and piracy anyway (including independent developers which can go ridiculouslypainful lengths of anti-piracy techniques). Valve also released Steamworks which further allows Steam integration of the game to Steam, but it isnt mandatory in any way. Its all up to developer/publisher for what and what not to include as Steam release. If Stardock doesnt want to use DRM of Steam, they dont want to, they can just release it with a steam overlay IF the game is being run by the Steam. If not, than in can just as normally as it runs from SDC.
I think all people know the real reason why Stardock doesnt want to release their game to Steam. Stardock considers themselves as a direct competitor of Steam. I am OK with that, infact i really respect and admire that. I think the people that are quick to bash Valve or Steam should also have at least some objective thought before considering it "rubbish".
As for the buying games from Stardock Central (or impulse if its released already), i made my mind while writing this post. I will be unhappy at first, but who knows if i like it i may migrate to SDC permanently someday

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Note: Sorry for the big wall of text and the errors i made in it. I'm not a native english of speaker