I think this is a standard feature of most modern touchscreen smartphones and not some "design brilliance" relegated to only Apple devices.

I currently have to carry two phones, one is an Android device and the other is a Windows Phone 7 device, they both implement the proximity sensor and it works the same way as the iphone.

IIRC correctly HTC (back in the days of Windows Mobile 5) already employed this feature in their "slate" phones before the original iPhone was released. They then improved it by adding some rather unique features, like being able to flip the phone over (i.e. laying screen side up on a table) to silence/reject an incoming call.