It's literally the app store logo minus the circle. But you're right, the same icon is also used as part of the generic app placeholder icon. In either case, it

It's literally the app store logo minus the circle. But you're right, the same icon is also used as part of the generic app placeholder icon. In either case, it does still belong to Apple. Edit: In fact, thinking about it some more, it's very clearly much closer to the App Store logo than anything else. It's literally the white silhouette design from the logo (as opposed to the colored non-sillhouete version from generic app icons), placed on a blue button that's similar to the app store logo's blue background.