I've often wondered whether people who use the internet are more likely to be douchebags, or if trolling the internet turns people into such cunts. It's an interesting question as we move forward and the percentage of people tooling around on their computer all day increases.
It's sad to watch as the internet culture moves toward this shared conscience that anything digital should be totally open and free. There are certainly merits to the widespread sharing that goes on, people have mentioned those already. Unfortunately, I feel like everything gets cheapened in the process.
Nevertheless artists and labels have to adapt. I'd say as soon as the album is mastered, fuck it get it on any and all digital download stores immediately. That being said, cram the physcial release with shit that cant be duplicated to give incentive to people who are willing to pay. I think this could help sales a lot, even if the unit price goes up. I'd pay top dollar for artist signed digibooks. While you're at it, release the discs in album sized books. I would have paid 4x for the SL digibook if it came in an LP sized book like Jethro Tull's Living in the Past record. I'd have that book on my coffee table permanently. Travis' art at that size...
Other things that might be more realistic to include exclusive to the physical release could be promotions like discounts on Opeth merchendise, links to demos or other studio outtakes/home videos. All of this could be kept exclusive with some kind of license key like video games have. One unique key per unit. Key's get shared, the key generators get cracked.. yeah eventually, perhaps. Judging from the anti-piracy posts in this forum I'd guess most of us who'd pay for these extras would be less likely to share then to just give you knob-slobbing pirates the one finger salute.
I speculate that Opeth is taking steps in the direction you are suggesting by releasing albums in 5.1 DVD mixes. Only problem is not everyone has 5.1 yet. I agree with you though, the book thing is a good idea.