Recent years have seen three big changes in the typical screen size used to view Web apps. First, more laptop and desktop displays are widescreen — shorter and wider than their predecessors. Second, most desktop displays these days are gigantic — between 1680×1050 and 2560×1600. Third, the increasingly-popular mobile devices use a wide range of screen sizes.
The net result is that Web app developers need to create apps that will work — and look good — on a huge variety of screen sizes and shapes. And in general, that means more presentation-layer work for your application development team.