One of the classy/awesome feature of an iPad, is the way the screen changes resolution/orientation as and when you rotate the iPad physically. The pages that you see on the screen switches between landscape to portrait mode just like that in a nice smooth continuous fashion.
Hence it becomes important for a iPad application developer to ensure that the page we develop for the iPads, looks good in all orientations and hence we definitely have to know where and when to change the application's styles.
For a simple panel created using using Sencha Touch, add the following property to capture the orientation changing event and you are set to go. Hope this is applicable to all components in sencha touch.
orientationchange : yourCustomFunction
Hope this helps :)