Mistwell
Crusty Old Meatwad
The problem with this theory is that it is too non-conspiratorial/non-stupid. What I mean by this is that if this was the case it would be easy for them to say that they are pulling the PDFs because they are not cost effective. While some people will complain about PDFs going away WotC wouldn't have the additional negative PR of being stupid or shady. Instead WotC comes up with the piracy explanation that makes no sense. So if not being cost effective is the real reason why hide it behind a fake story about piracy. If they are going to use a fake story, conspiracy comes to mind before a belief that they are too stupid to not use the real and innocuous reason.
1) You are assuming they have ever directly commented to the reason for pulling the older edition stuff.
2_ And you are assuming that they have even seen any actual negative PR from the non-4e stuff. Remember, they see the actual numbers for sales, and they may well know something we do not - that non-4e PDFs sold virtually nothing relative to total sales, and anger over the issue is viewed as just the same people who already hate WOTC taking another opportunity to complain about something WOTC did.
As for #1, from what I have seen, they have responded to general questions about the pulling of all PDFs, and for that their primary answer is piracy.
They have briefly commented about older edition stuff, but only to say they don't plan on offering PDFs, and not to explain why that portion was pulled.
So I think the two are not mutually exclusive. They can pull all PDFs in general due to piracy, and specifically the older edition ones because the hassle was not worth it (IE they were not profitable enough to justify splitting 4e from non-4e PDFs and continuing to sell the non-4e PDFs).
And they can dismiss "negative PR" if they view it as just the same people who were already angry and not buying their products just expressing more anger.