It is meant to be a scientific study. What's the use of an unsubstantiated claim? In fact, its been proven to be highly counterproductive (at least in other fields) as others go on to build works and further claims around it, only to later discover the errors and depth of uncertainties.

Using the same principle, I could posit (probably quite defensibly), that the amount of alleged copyright infringment of Megaupload Limited's limited access and centralized services would be dwarfed by that from Bittorrent and other P2P methods.

These claims are just conjecture. I mean if it is ok for a scientific paper to be made up of unproven conjecture then I guess it is fine.

"But are these the claims really that outrageous? ie. The biggest piracy site in the world has a slight effect on sales?"

Well, there has been some evidence pointing towards there being a positive effect on sales. So not outrageous but controversial still.