I don't know about US law but at least in Germany it's really like pointed out.
There is a law governing TOS terms, and it says among other things that the TOS can't contain unexpected und unrelated terms.
So if you write for example into the TOS governing your website something like that every visitor owes you 1000 bucks that won't be enforceable.
The TOS related legislation is nothing new. It was there already in the analog age to prevent companies form tricking people into signing inappropriate contracts.