Many years ago, I ran across a good icon design tutorial. It said that having unique contours to icons help users scan for the item they're looking for. If this is true, why don't iPhone and Android app icons use unique contours?

iPhone

iPhone icons are all rounded squares. The only visual cues for zeroing in on an app is the inner design. I don't know about you guys, but sometimes it takes me 5 seconds to find the Map app.

Android

Android icons only have a few contour variants: square, circle, talk bubble, ... In my opinion, Android's limited set of contours is worse than iPhone's uniform contours. It tricks people into utilizing the contours to help them parse, even though it won't help them. For example, I'm often confused when trying to find the music speaker icon because it has the same concentric circles as the camera and settings icon.

Windows

What ever happened to good old fashioned Windows style icons? I think Window's icons elevate scanability over consistency / style. I never find myself aimlessly gawking at Windows icons because almost all contours are unique.