It's also a kind of Steam for drivers, if you will, in that it automatically maintains an updated list of drivers for your PC's various parts, only requiring the user to click the install button.
For weeks now, Blizzard has been offering pre-purchases of the game online, and you could download Diablo 3 in its entirety before release in order to simply click a button and install on launch day, and customers can continue to buy it through them at any time since then.