@androidi: technically, the specifications do not forbid a 4:3 aspect ratio as long as it meets or exceeds the requirements (e.g. 1440x1080). Also, those requirements are for getting the hardware certification; in theory OEMs could just give that up and do as they please.

Regardless of the respective advantages, requiring a 4:3 aspect ratio would have most likely resulted in the same resolution of the iPad, which would have been unwise for a latecomer (ah, the irony).