darkplanetar: so they will not close the site 10-20 years? i hope...
Coelocanth: Who can say? Will GOG? Will Steam? There's no way to tell. If that's your worry, back up your games.
These are subscription services. If a vendor bites the dust, your games are practically lost.(see Direct 2 Drive incident)
You cant possibly back up hundreds, or God forbid, thousands of games. And proof of purchase helps when the police come banging on your door, but otherwise its just there for that warm comforting cozy feeling.
After the Direct 2 Drive->Gamefly fiasco i only buy game.. subscriptions ;) from digital retailers(or keycodes that can be redeemed in said stores) i feel that will be with us for a loong long time. That means Steam, GamersGate, GoG.. and thats pretty much it.
The most dubious of stores i feel are the random bundle/indie websites that appear from nowhere. I wouldnt be half suprised if all indie bundle webpages(including Gala, Bundlestars, and Royale) gave me 404 in 1-2 years. Except Humble of course, that project grew out of indie space long ago.