Neowin posted a story that Windows 8 apparently now includes a way to close Metro style applications just by touch gesture

You might think that closing Metro apps in Windows 8 would be handled by touch gestures. However in the public developer's preview version of Microsoft's upcoming operating system, closing Metro apps is handled by the Task Manager. Now a new video posted by the WinUnleaked.tk web site shows that a new Windows 8 build has put in touch gesture support for closing Metro style applications.

As you can see in the above video, dragging the app via touch down to the bottom screen shuts down the application in the Metro UI version. The video itself is of very low quality; it was clearly taken with an outside camera filing a screen.

  Windows 8 now includes touch gesture to close Metro apps