[mmis1000]

I don't think valve ever tried to do that seriously. Even games checked purchasing status via steam api at startup are usually one dll away from allow it to run completely locally. They don't say them allow it, but don't seem to seriously fight against them either.

I think what they sells are more about services that support the game. For example: you can find l4d2 crack easily. But you are never able to join to the official community server list without a proper purchase.