Contracts fall under civil law. There is no statutory definition of what constitutes offers and acceptance. So in this case, were I a lawyer, I'd argue that the TOS is a legal contract, and by using the site, you have implicitly agreed to the definition of contract acceptance specified in the TOS.

Whether it holds up in court is a different question, but this lawsuit at least gave a precedent.

Do you have any examples of implicit acceptance of arbitrary contracts merely through accessing a network resource?

Of course not - The contract would be made when money was exchanged, not when the site was accessed.

Sure, but the money is exchanged between kickstarter and the participants (backers and makers). The participants don't exchange directly with each other.

Yup, that is a likely counter argument to be made in court if anyone ever sues over these issues. As I said, though, this is civil law, so it would come down to how lawyers argue it and what judges think. In civil cases, answers are rarely black and white.