Sure, that would discourage such an affiliate.
Just how many people do this though?
I would never promote a program with a quota, what happens if I fall out of google, or get sick or something? Then they quit paying what I worked for and am owed? Not gonna happen, this business is risky enough without a clause that can send me to the poor house should I have some issues that keep me from delivering more and more. I want to get paid for what I deliver, period.
And of course, the retroactive issue stands. Breach of contract is just not acceptable to anyone, including the legal system.