Just to add something to the mix here - WotC products aren't the only ones being pirated - Adamant Entertainment has reported previously the availability of their entire catalog in the torrent channels, and I have personally seen torrents of the entire Paizo Pathfinder catalog. Granted, neither of them is the 800 lb gorilla that WotC is, but I would think the impact would be even more profound with Adamant - and they are still in business, and still getting income from PDF sales (I have no data on the level of said income, good or bad).
What about Green Ronin, Mongoose, White Wolf? I'm pretty sure they've got pdf products being pirated as well. Why have none of these other companies taken drastic actions to combat this menace?
Interesting question, no?