Thank you. I don't think I'm being stupid, but you have made me think about it a lot, so I appreciate that. You are right that the online marketplace is not a fixed resource, that's not technically right at all. I was thinking for a long time, "did I misunderstand that?" I certainly didn't think about the input vs output aspect of production. This led me to do some more reading and here's what I've got.

I do still think Steam is factor of production in that it is a capital good, like a business complex. The problem with your outputs argument, I think, is outputs are the quantity and quality of goods or services produced in a given time period. Well, for the devs, there really isn't an output in the traditional productive sense. They didn't produce a bunch of cars, creating X amount of value through their labor. The value is only created when copies are sold, and in that sense Steam,, and other game stores are inputs in the value created by a game dev. I think one could even make an argument that publishers provide a service and Steam is involved in that as a factor of production, but I think that speaks more to the strangeness of the software market in general. Anyways thanks for actually taking the time, I got to learn some cool stuff and feel a little humbled in the process so that is good