It's an interesting situation. It could be assumed that everyone sees that, and then perhaps not require proof that the person saw that statement. However if you apply that same logic it could easily be assumed people aren't actually reading the Terms, and so how could that be allowed to be binding? It is technically possible to have a time-check to see how long someone has spent on a Terms of Service page (if any at all), so there couldn't be the excuse that it is impossible otherwise. I suppose it would come down to a judge deciding who should be allotted more protection, and hopefully for the benefit of society. I imagine there must already be case law that says one way or another.