Again - I don't see them saying that. Back clicking is an incredibly natural user activity, for example... they see results, click on a result, view it for a second, back, click on another, view it... (paid and natural) and then click again on the original paid link.
That's not fraud. It's invalid clicks.
99% of search users don't have a clue what the differnce is between the two types of click. But I know this much - even if I am not first in the organic results, I'll get traffic. Why? because the user doesn't go to the first result? no - because she back clicks, to quickly decide which site is right for her. She'll end up double clicking on organic results at a very similar rate to paid, I bet.