It's a fact that the size of smartphone screens is increasing gradually with sizes above 4-inch currently the sweet spot; the HTC Touch HD, the HTC Desire HD, the Sony Ericsson Xperia arc, the Samsung Galaxy and the Motorala Atrix being the ones already announced.
Now with the launch of Honeycomb, Google's tablet-optimised operating system, and the company's reluctance to commit in the long run to two Android forks, we are likely to see Honeycomb on large screen smartphones with Gingerbread gradually fading in the background.
With a native resolution of 1280x768 pixels, Android handsets may well encroach on Apple's iPhone 4 territory by offering Retina display equivalent pixel density. A WXGA smartphone only needs a 4.5-inch screen to surpass the iPhone 4's pixel density.
Tens of millions of iPhone 4 and the iPod Touch have been sold worldwide all of them equipped with Retina screens; this has considerably depressed the cost of manufacturing such displays since the capital investments have already been made 18 months ago.
Using a single, unifying user interface, makes the life of developers easier which is why Apple's iOS is the same across three different platforms (soon to become four).