Yes, the book is an e-book, not available in print. As mborn says, it keeps the costs down. I have some info on my website about it I'll paste below:

The reason for sticking to digital is three-fold.

First, it keeps the costs down. The books are large and full of colorful photos and illustrations – making them very expensive to print. Last time I checked, it would raise the cost on your end to over $60 or more – plus shipping.

Second, digital makes for easy updates. While some books don’t see updates very often since the information in them isn’t subject to change due to technology (like Secrets To Stunning Wildlife Photography), some books get updated far more frequently.

For example, the Nikon AF book was updated twice for new cameras within the first six months of publication. The new book will see an update soon as well for a some typos and clarification corrections. Plus I have some more info I'd like to add to the Exposure and Metering book as time goes on.

With digital, these updates are free and easy; with paper, not so much. Plus, if I did issue a new update, everyone who purchased the book in hard copy form in the last month or two would want to return it for the updated version. Digital makes the update much easier.

Third and finally, it’s easier for me.

OK, I know that’s selfish, but the truth is, I don’t want to deal with shipping, damages in transit, and any printing issues. I’m a one-man operation and have more projects in front of me than I can ever finish.

So, digital saves me a ton of time and allows me to continue to write books, articles, and produce videos.

All that said, if you do want a hard copy, we’ve had people take the book to a printing place (like Kinko’s) and have it printed and bound. You are welcome to do so for a single copy for your own personal use.