please note i say all this as someone who would much prefer a non-tapered phone with symmetrical top and bottom bezels:
realistically the taper looks subtle enough that it probably wouldn't functionally hinder the phone in any substantial way, even comfort when holding in landscape. likewise with the asymmetrical top and bottom bezels.
the 6 million dollar question (provided there is even any truth to the rumoured design) is what does it add to the phone? right now it feels gratuitous change for the sake of it. but so did the broken metal bands when iPhone 4 first leaked. then it suddenly seemed like a stroke of genius when they revealed it was actually the antenna wrapped around the perimeter of the phone. of course whether that was ACTUALLY a good idea is a whole other debate, but at least there was clear motivation. and the motivation contributed a lot to its perceived elegance.
if i had to make a guess at the design justifications of the rumoured iPhone 5 based on their past choices, it would be as follows:
-They want a larger screen to compete with some of their competitors, but they needed to keep a certain amount of bezel, so they had to increase the width and height. the iPad is a good precedent that they continue to believe bezels are important.
-They don't want it to be considered an oversized brick, so they push to make it as insanely thin as possible to compensate. pretty much their entire company history is a good precedent for this behaviour
-Decent camera components just don't come that thin. (Precedent: iPod touch. They abandoned their first attempt and then eventually settled for a lower quality camera that left many dissatisfied.) So they taper the phone to be a little wider on the top to fit it all in, while still boasting about how thin it is at its thinnest point. Marketing precedent: macbook air
Anyway, I'm not saying you couldn't argue the objective sensibility of many of those points, but i do feel they all "fit" with apple's M.O.