I feel for you, but the publishing business imo should have offered considerably discounted, or even free ebook versions with their print versions. Since ebooks became a reality a few years ago that's what I have been asking. They wanted to go all digital to reduce their costs drastically and become like the music business. Sadly they didn't understand that no one can tame the web and people are going to find most of their books for free too. Can you blame people for "stealing" an e-version if they already own the printed book and they are not given the benefit of an e-version of it?
I agree with this point and the one above about DRM. Without going into the specifics too much, my company saw this coming years ago and started electronic distribution long before Apple and about the same time as Amazon. We also aggregated the the rest of our industry to use our site. In order to do that, most of them demanded DRM.
Once they became comfortable with selling books online, we then moved them off of DRM (very similar to how Apple did it) and into a non-DRM "Watermark". The books are distributed as non-protected PDF's, but your name and order number is placed visibly on some pages and invisibly on others. Use it on any device you want (including the iPad), but don't distribute the files with your name on it. Of course the names can be removed, but for those wanting to do the right thing, it is more effort than it is worth.
Those who want to steal will find a way around any DRM anyway. The goal is only to make it obvious to those who "inadvertently" share because they actually don't think they are doing anything wrong.
As to the other issues, a shared digital copy is difficult with a mass-printed book. Where do you put it that the code cannot be taken out of the book and used? In order to do it, you have to shrink wrap or seal the book (and who wants to buy a book they can't look inside). I suppose you could glue a CD with the book, but now you have increased your costs (and kind of crapped up your nice book) and given people an "accidentally" distributable version of your book.
We do have a service where we offer softcover books printed on demand and shipped to you. These also come with a digital copy you can download immediately because we can verify that, in fact, you ordered the book.
I actually don't blame people for downloading an digital product to match a physical version they have purchased. If only everybody were so trustworthy.
It is a little easier for us because we are a smaller company and easier to maneuver and make decisions. The big publishers have so many contracts, individual legal requirements as well as localization issues that these are hard issues for them to navigate.
FYI, not as a plug, but just because I am sure some of you are wondering what this site is, I am including a link. We sell hundreds of thousands of books a year.
http://www.drivethrurpg.com/