It seems clear to me that owning a digital copy of a book provides a number of additional benefits that you would not have simply by virtue of owning a printed copy. Those are benefits that you have not paid for as part of your book purchase. So why should you be automatically entitled to those benefits without paying for them?
Certainly it has advantages, or no one would ever want a digital copy. Some of us just think that it's far, far better for consumers if what we're buying is the ability to use a product as we choose, as opposed to only in the way the company that created it chooses.
For instance, let's say I buy a digital download of a movie that grants me what is generally understood to be the perpetual ability to watch this movie (For instance, perhaps the service compared itself to purchasing the movie on VHS.) Because it is protected by Windows-specific security features, this digital download is only compatible with a Windows PC.
I later decide to purchase a Macintosh. It would then seem clear to me that owning a Macintosh-compatible copy of the movie would provide a number of additional benefits (for instance, being able to watch the movie ever again) that I would not have simply for virtue of owning a PC-compatible copy. I feel they are, however, benefits that I should be entitled to as part of my purchase, same as I feel entitled to rip a CD of music or VHS movie I own onto my PC,
especially if the CD or VHS is showing signs of damage and is soon to become nonfunctional. (Heck, I just did that the other day - one of my CDs was scratched so bad it was playing the wrong tracks or jumping tracks mid-song half the time, and it took me about five tries to rip a working copy of every song on it.)
The text search and copy/paste are about the only issues that have merit, because they're actually an advantage you won't usually get if you scan the book yourself.
(Well, maybe also the effort part. As someone who's actually scanned and OCR'd an RPG book for his own use, it's not a negligible effort - I spent the better part of six hours on the darn thing and was using about $350 in equipment and professional software above and beyond just PCs, and I intentionally destroyed my book's binding in the process because I wanted a professional-quality digital copy more than the hardcopy book.)