It's a digital version of the game that can't be shared, sold, or transferred to a new system (generally).
If they [all digitally downloadable games] were cheaper than a physical copy, I get it.
So why the hell aren't they?!
Who buys a virtual copy of a game for full value? Would it make too much sense for the DD to be like 20% off?? I guess they make their money off the suckers that download games and are stuck with them and can't trade them in. I've downloaded a game before and instantly felt like an idiot.