Eh. I have an honest question.
Why shouldn't WotC charge a "nominal fee" for such things?
For those who don't want to pay it, you still have the book--exactly what you paid for, and exactly what you would've gotten if the DDI didn't exist.
But if WotC is offering extras such as an online copy of the book--and that is an extra, above and beyond what anyone has any right to expect when buying a hardcopy of said book--I believe they're well within their rights to charge for it.
I agree that I certainly wouldn't pay full price for the same book twice. (Not that WotC's given any indication they're charging anywhere near that much.) But even if they did, I wouldn't be "outraged." I just wouldn't take advantage of the option.
If it's a couple of bucks per book, that's more than reasonable, given the average cost of electronic/PDF books in the industry.