"Market makers" are a very important economic function. Just because it's hard to put your finger on a tangible product, the fact that they were able to create a unified framework for selling games to customers is worth quite a lot of money. A lot of people had tried (and failed) to do similar things in the past. Those things you mentioned are almost irrelevant. The actual value they're delivering is being able to easily and economically distribute your game to a wide audience and, as a consumer, connect me with a large number of games. It's like trying to say the value of a road is the stopsigns and traffic lights on them, not the fact that it's connecting two cities.