Yea, actually it doesn't hurt you argument at all; if anything it helps it. The article's author speculates that:
Were seeing once again that music lovers will get their content one way or another, and if they deem it worthy of support, they will buy it. This process includes sampling and discovering content, and in todays age, piracy is one of the best ways to do it.
So if he is right, and the downloaders are generating sales by sampling & buying, blocking piracy will reduce the amount they will buy.
I agree with you, I don't think six-strikes is going to make a noticeable increase in sales.