Since cutting off legal access to PDFs won't diminish piracy at all I think you're wrong, Ryan - unless WotC's decision makers have missed the last 10 years of internet piracy.
Given that I do not think WotC's decision makers are that stupid I think this is not piracy-related, but related to remove legal access to older editions.
Yeah, I'd think if anything this will encourage piracy of WotC products.