The Snapstick app also had an button to launch apps, which at this point were limited to Pandora, Skype, and a terminal program we presume won't be present at launch.
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.