As noted in an earlier FAQ, I've moved to all-electronic distribution.
Physical products (CDs) are treated differently under law than virtual products (downloads). You may have noticed that you have to agree to a license agreement every time you download something, including from this site. If you're ever read that license agreement carefully, it basically says that you're renting the product, not buying it.
When you buy and receive a physical product (CD), the legal premise of First Sale applies, something that was a given with paper books in the olden days, but is getting lost in the digital era. When I started selling eBooks in 2001, I wanted my works to be treated just like a paper book. That meant that when you were done with it, you could pass it on to someone else, or even sell it (you couldn't legally retain any digital copies you made, just as you can't legally retain a Xerox copy you made of a paper book).
As many people have discovered over the years, my CD eBooks retained residual value over the years, just as my paper books did (one out-of-print book of mine has been selling for eight times its original price on eBay). When you sell your camera to upgrade it in a couple of years you’d find you'll get a few dollars more for it if it includes things like one of my Complete Guides on CD.
With the new site now in place, I've moved to download-only because so many of you are immediate gratification freaks and keep asking for it. I’ve also downsized, and we no longer have the office and warehouse space to handle physical inventory. Frankly, I'm not in love with the change to all digital downloads. It means that products become much more ephemeral. Still, the vast majority of you asked for downloads and I've decided to comply. Just be careful what you wish for. Downloads are not the same as physical products and thus have no residual value when you're done with them. You cannot sell your downloaded eBook when you are done with it. Is that really what you wanted?