Folks on EN World have, imho, an overly optimistic view of the pdf market. Yes, lots of folks here, on EN World, like pdfs. However, I have seen no credible evidence that the bulk of RPG players make use of them. I think the market for them is much smaller than many might expect.
I have seen lots of credible evidence that suggests rather emphatically that the bulk of RPG players do _not_ make use of PDFs.
But I've also seen credible evidence that there are a lot more RPG players buying PDFs than there were three years ago.
And I think a huge percentage of PDF customers fall into one of these two categories:
1) Folks who ALSO own the print edition, but who want a portable, easily searchable reference copy.
2) Folks who do not want to risk paying full price on a book, and use the PDF as a way to "taste" the product to decide if it is worthwhile to purchase the print product.
I still feel very strongly that the bulk of the PDF market is SUPPLEMENTARY to the print market. I think the customer who "only" buys PDFs, or who even prefers PDFs, is in the minority of the PDF market.
As technology and e-readers get better and better, I suspect this to change, but if you want to make decent (or even "much of any") money in this business, you still need to print books. PDF sales is just the gravy on top.
Of course, if you can't afford to make a full meal, getting by just on gravy is a lot better than starving...
--Erik