A while back they updated their service provider agreement to require users of steam agree to arbitration rather than court action.
The problem is that a user could not access their purchased games even in an offline manner until they agreed to the new terms. I was presented with the new terms, and clicked "I disagree" and Steam immediately exited.
I even wrote Gabe about this because I found it fundamentally anti-American.
I'm no lawyer, but I could see that forcing someone to agree to terms by withholding "property" they have legally purchased would not be enforceable.