How is that even supposed to counter what I'm saying?
What you said is:
You can't add non-Valve games to Steam.
What I'm saying is:
You most certainly can, there are nearly 100 non-Valve games whose physical box copy serial keys can be registered onto your Steam account.
You can't go add random games on steam and have them activate. It just doesnt work. People keep QQing about origin doing the same thing.
Obviously steam set up something with said publishers with specific games. (From what it looks like those games require steamworks) Such as a game like Black Ops or Modern Warfare 2.