why the price of the pdf/epub version is the same as the paperback?
The paperback also requires an additional $3 postage, so it's actually $22 instead of $19.
That's the idea. If you can't afford a $19 book you're going to have a hard time starting a software business...even a one-person operation.
But you nearly had me! Throwing in the PDF was a huge motivation to upgrade. I think (if I may be so bold) that you should throw in the PDF with all paperback sales, and make that obvious on the homepage, eg:
[Download Sample] [Buy PDF $19] [Buy Paperback & PDF $24]
Re-reading chap.1 is on my list for today and then I'll buy the PDF.