My expertise and narrow FOCUS is in human factors and ergonomics. I'm Zephyrnoid in the Blogsphere but only on the Blogsphere 😀...elsewhere.....
16:9 is a fabulous ratio, albeit, the NEW GOLDEN RATIO. Whereas 4:3 was the Classic and ancient Golden Mean, ideal for architecture, the 16:9 is perfect fit for electronic text and movie content TOGETHER.
I addressed the advantage of a vertical 9:16 for reading elsewhere in this thread. I am NOT about to dig up citations, you can do that yourself via Wikipedia or a Google search. Simply put, the MINIMUM human readable and comprehensible line of text and font size results in the double newspaper column. Too small for you? No prob, flip the tablet around. Still too small? Zoom it.
My MAJOR gripe with RUMORS about the ipad mini are not so much the 'boxier' than 16:9 ratio but rather that we may end up with a tablet that may be smaller than the current ipad, but will be too large yet for a number of uses and coat pockets.