Right now, I if I buy a paper copy of a book, I own it. I can read it, burn it, sell it. Fast forward 20 years, I can still read it, burn it, or sell it. If I buy a digital copy, I *should* be able to read it today, I might not be able to read it in 5 years, and in 20, I'll be lucky if it even opens on what ever gadget is being hawked then. I will never be able to sell it - and burning would be a bit pointless.
That might be fine for a beach thriller, or a newspaper, but for a serious book I intend to reference for a long time, it is NOT acceptable.
Now, the same thing applies to games. I still, if I wanted to, could go back and play Ultima Underworld, Daggerfall, Morrowind, or Deus Ex - because I own the game discs, and can install them any time I wish. In 20 years, with the right emulator, I could still play them.
Would I still be able to download and activate Fallout 3 in 20 years? I'm going to guess not. I'll be surprised if you can stlil activate in 5 years. It's an indefinite lease that works because most people get bored of stuff so fast, and don't even realize they just paid $60 for a rental.
If I wanted to rent stuff, I'd expect to pay a LOT less, and get a definite time period. Paying full price, and not knowing exactly how long the rental period is annoys me.
Digital data is copy-able. Forcing restriction on this data is impossible, that's why pirates exist. Removing restriction from this data but binding the ownership to an account is the real ownership. Every Steamworks executable is generated for your account, it is unique to you. You do own something to your own this way.
Now if your book was burned or got loss in midway after 10 years and 20 years later when you look for it, what will happen? You will search a copy just to find out it is out of order. Your best bet will be finding a digital copy.
Unreal
Half-Life
Oddworld
Doom
JK:Dark Forces
Riven
Quake
MDK
Kingpin
Hexen
Heretic
I can play all thanks to Steam in XP and 7. Steam even handles Dosbox emulator if necessary so I don't have to. I completely rely on Steam so I can play my favorite games 20 years later, above is a case in point.