I reckon it'll cost them sales
When 4th edition first came out, I was underwhelmed. I hadn't been impressed with 3rd edition (sure, they tried to fix things, but multiclassing worked very badly for spellcasters, and it didn't feel like D&D). A friend "obtained" them, somehow and lent me the cd. I liked the look and so went and bought the 3 core books, as did at least two others...
So that one download gained them sales of 9 hardback books.
They might be counting on the brand having built enough support now not to need such encouragement, of course, but it seems rather negative...
And it's really not possible to play from a pdf - the proper printed version is so much better to hold, and easier to use - but the pdf is handy for looking up specific rules...