Have you used a 16:9 tablet? I have. It's fine for horizontal use, but awkward when held vertically. What exactly is a "normal" aspect ratio, anyway? Can you point me to an industry standard link that defines what "normal" is?
IMO 16:9 is a pretty good ratio for tablets - I own one, and when it's horizontal it's perfect for movies (where the iPad has to have letterbox bars) whilst the vertical orientation is perfect for books & PDFs, as the 16:9 ratio is more the shape of a book than the 4:3.