GameSalad are another game creation company who has confirmed support for Windows 8 App Store publishing via GameSalad Creator Pro.
Once GameSalad Creator for Windows 8 is released, you will find a new "Windows 8" publishing target integrated directly into the web publishing flow, allowing you to quickly and easily publish any previously developed game or application to the Windows 8 Store.
GameSalad and Microsoft will be hosting a joint webinar for any developer (basic or pro users) interested in Windows 8 Store publishing on Friday, September 28th at 1:00PM CST. Please register here: https://www4.gotomeeting.com/register/452117663 - Introduction to the Windows Store.
Updates on GameSalad and Gamesalad games now in the Windows Store blogs.msdn.com/.../gamesalad-amp-creating-games-for-windows-8.aspx