A recent report stated that fragmentation on the Android has caused a drop in the number of developers interested in developing for the Android. Fragmentation means something different for each person. It could be the SDK version, or the screen size, or the processor speed of the phone, although the last one should not pose a problem for any half decent developer.
Sure, there is no denying that to program for a single screen size and resolution makes the developers life a lot easier. A bitmap is easier to handle than a vector, absolute numbers easier to understand than relatives, and you know who big the text will look on your customers devices, because their device will be the same size as the device you are developing on. Also, the OS user experience is smoother because the OS does not have to cater for a variety of different phone attributes.
So that’s basically the pro’s of a one size fits all approach.