I'm new to mobile phones development, but I have background in pc games programming. In my experience different screen size is problematic when writing games, and on the mobile the number of different sizes is large. I guess that a compromise would be that the models with the largest size (pixels) would suffer from not being able to use its screen to its full potential for compatibility reasons. This is specially true for pure 2D applications. On the PC this is easy if you use 2D in 3D graphics. Seems strange to me that there isn't any big list of screen size for most mobiles aimed at developers.