VALVe themselves have game IPs they want to protect. Within the boundary of "it's legal, wygd" there are always ways to make pirating VALVe games easier and VALVe will stand no ground to ban those.
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.
Name one instance when Valve showed even a fraction of the amount of aggression Nintendo shows to protect its IP. Pirating Valve games has always been easy - it's as easy as copying the game folder anywhere else and running the game executable.
When you are confident in your own products, you don't have to stoop to cheap user-hostile bullying tactics to protect your wares.
Nintendo: "oh no, how dare you show that your product can do something that's perfectly legal and a very common use"