This is the only way that permissions should be implemented by any mobile platform. Without it, users are forced to decide at install time whether the payoff of having the app installed is worth the associated risk of granting ALL permissions the app requests. It's a hard choice to make before you've even installed the app.
Jeff Atwood describes the app-installation-headaches nicely here: http://blog.codinghorror.com/app-pocalypse-now/