I am developing a web app in ST2 PR2 and it has whitespace at the bottom of the screen on my HTC Desire when using a fullscreen viewport. I thought it may have been my code, but the same thing happens if I view your kitchen sink demo on your website on my HTC Desire. My phone is running Android 2.3.3 Gingerbread. I also tried resetting the browser on the phone to default settings and that did not help. This whitespce is present at the bottom of the screen in landscape and portrait views on the phone.
This is down the to autoMaximize method in Ext.Viewport which tries to hide the address bar when it exists.
In the next release we have decided to change the default value of this to false, instead of true. There are just too many situations where there are issues with the viewport not expanding. Not to mention the fact that the performance is slightly worst when it is enabled.
If you ever want to enable it in your application int he future, you can use the following configuration in Ext.setup or Ext.application: