gameon: ... Surely if they weren't working out, GOG wouldn't be adding so many.
That is a good argument in the long run but not in the short run. They are adding Indies for half a year now, it's still like an experiment. But experiments can fail. Let's see if in one year they are still adding Indies at this rate.
Also GamersGate are also adding these Indies and even more games (and many of the "more games" are kind of crappy) but they said at some point that most of their games have only little impact on their earnings and vice versa.
My guess is that with high priced AAAs reluctant to go DRM free and classics not being available in large numbers Indies are the only option to go, even if it turns out, they aren't so sellable.