When you test multiple Windows devices you quickly hit the 5 device limit on Windows Store accounts. Even if you don’t test lots of different devices you can still run in to the limit by the time you have install apps on a Windows Tablet, laptop and a few Media Center Systems. From October 9th you will be able to install apps on up to 81 devices from your Windows account, so when you get a new device you don’t have to deactivate other devices. This is a smart move to remove the five item limit and will apply to Windows 8 and Windows 8.1, so you can that extra Surface device and install Halo Spartan Assault on it.
Via the Windows App Builder Blog