Bedrockgames
I post in the voice of Christopher Walken
There's a strange contradition about PDFs and how many people will use them (on screen or print them out). On the one hand, some folks will say that WotC can't make money on them, yet when they were available WotC was constantly atop the best sellers list on the top ePub sites (and acceptance of electronic products just keeps exponentially growing, if things like tablets and readers, and the demise of so many B&M stores, are anything to judge by) and on the other hand apparently piracy of current edition books at the time was enough to cause WotC to completely reverse their policy on all PDF products, even older edition (but if nobody wants them or will use them, how can they damage the profits?).
So, lines like "The pdf's never sold in numbers to actually matter all that much" really doesn't track for me.
As for 4E support once 5E is out, and compatibility of 4E with 5E? I think those situation will be in line with 3.XE support once 4E was out and 3.XE compatibility with 4E. It's a matter of bolstering the value of the most recent edition.
I think it was definitely not a bad revenue stream for WOTC. And PDFs, when priced right, are a great way for companies to make money (some RPG publishers are striclty PDF because of the lower production costs). In WOTC's case I think they simply crunched the numbers and decided the risk of piracy outweighed the financial benefits. Since then PDFs have only grown. I don't know if they would reverse the decision or not though if they had a chance. I think from WOTC's point of view I think they were spooked by the large number of free copies of their books available online.