Design for Mobile Ain't that Simple

Most companies, including design departments and agencies, underestimate the amount of work that goes into graphical design for mobile. Indeed it should be estimated much more time because where as for the web the developer can "chop-up" the design images once and use the pieces for any display size, for mobile applications the design has to be specific for several display resolutions and sizes and resizing of the original is a bad idea that ends up in a lower quality product. On top of that in Android you don't "chop up" the images, but you create a custom, single "9patch" stretchable image, which make life easier, but hardly any design artist I know knows what it is, and how to do it.

Uki's Google Java Technology blog