In the early days of WPF and Silverlight, the only way you could get information about the default templates and styles of controls would be by opening Blend and editing a copy of the default style. Fortunately, this information is now documented on MSDN, however it is not always easy to find. In order to make it easier to lookup, I have made this list of all the MSDN articles about default styles and templates for Windows Store Apps controls:

Note that you will also find those default styles and templates in the following file on your disk: C:\Program Files (x86)\Windows Kits\8.0\Include\WinRT\Xaml\Design\generic.xaml.