i[Contracts are fairly easy to breach if you have a good lawyer, and I imagine Valve does.
Do you have an example to back this up with? This sounds like wishful thinking. Money is the easiest way to break out of a contract. You pay the other person enough and he'll walk away happy. You don't and he'll take what you owe him. ]
Parkes 100 v Kartes
Katz v Danny Dare, Inc.
It takes a good lawyer to write an airtight contract. And a better lawyer can poke holes the size of a minivan through it. Especially on something subjective, such as whether or not something was de-emphasized.