Apple showcase of the controls that come out-of-the box and various ways to tweak them: http://developer.apple.com/library/ios/#documentation/userex...
Default Android controls for some reason sport a more "circa-1990 MS DOS" look. The developers need to actually invest time to re-skin the components or make their own to get a modern look. This is made slightly more difficult if you want to support multiple screen sizes/resolutions. As such, many Android apps sadly seem to end up with the default look.
(I have written apps for both platforms.)