i guess you have a point. i figured games a few years old have less chance of making their way onto steam, and since this topic started back in 2012 i figured it probably won't happen. But on the other hand, I don't think running in a browser would be much of a hindrance to put it on steam. It was mentioned above, but Realm of the Mad God started off as a flash-browser game. I remember first playing it on a website that hosted flash games. Then a few months down the road it got greenlit on steam. From what I observed it appeared to be the same game with very minor changes.
Game only came out in september last year, so it's still "pretty new" considering. Also, as you mention there's been several games, like Don't Starve, that started out as browser games, but that being said - a separate client is a matter of time and coding.
They just released "Game Dev Tycoon 1.5" on Steam, and that was made in 2006. Age really isn't a factor. It's really up to Jon and company if they want to create a standalone client for Steam and go that route. I have no doubt that it'd be great, but they're a small team and already have a lot on their plates
A stand alone game client would be a nice. But from what I have heard, there are problems with Greenlight. Quite a few games that were just terrible have been let through including Revelation 2012 and recently Guise of the Wolf.
