My primary addition to his comments is that I'm hoping this doesn't kill the traditional means of installing applications. While to some users installers, dmg images, etc. are confusing and can cause mis-installations (wrong locations, running off of the images, etc.) for many corporate, enterprise and educational customers, having the App Store can be a security and privacy concern. Personally, I removed the App Store from all of my images at the school.
It will be nice to tell grandma that she can just download using the App Store, though.