I don't believe that PDFs will
ever replace printed books in the RPG industry. A lot of people hate reading books onscreen. A lot of gamers aren't an active part of the Internet community and don't know about them. The PDF market is a
tiny fraction of the RPG market as a whole, and while it's a growing one--and will, I'm sure, continue to grow--I honestly don't think it'll ever grow to a large enough segment of that market to support the industry on its own.
Besides, when you tally up all the different factors, PDFs
aren't more cost-effective than print books.
*Waits for the screams of outrage to die down.

*
Think about it. You still have to pay for writing, art, development, layout, etc. What you're saving on is printing and distribution costs, and that
is a massive savings, certainly.
But the truth is, you can't sell PDFs for nearly the same cost as a print book. People have tried it on DriveThruRPG, and while they've sold
some copes, the vast majority of replies have been in the neighborhood of "What the hell are they thinking?!" When you combine the narrower audience for PDFs with the fact that you
must cut down the price of a PDF dramatically from a print book, you're right back where you were--in an industry that really doesn't make very much profit.
There is, unfortunately, exactly one way and one way only to turn the RPG market into a truly profitable endeavor, one so profitable that it might actually be possible to drop the costs on books. One way. And that is, figure out how to increase the size of the market by a
substantial amount. Nothing else, ultimately, will do the job.
If you could convince Hasbro that the time was right for a new D&D cartoon, that'd be a good start.
