Implement IsCancel and IsDefault properties on Windows.UI.Xaml.Controls.Button
In WPF, buttons on a form or popup can be specified as IsCancel to close the control with the Esc key or IsDefault to close the window with the Enter key. This ability has been around in Windows UI frameworks for some time, but it is not present in Metro style apps. I would like to see this common pattern implemented so that developers won't feel the need to roll their own version of it.
Joe White commented
The Windows 8 installer uses default buttons, and it uses a Metro theme. I can't imagine why Microsoft didn't make default buttons available in WinRT when they use them themselves!