Sounds like Win+... shortcuts can be "overwritten" by an application then. Maybe an API that has changed with Windows 8.
I don't think there's any changes - it's just that Win8 added more Win+X shortcut keys.
AutoHotKey (and probably AutoIt?) is able to override the shortcuts that Windows (explorer.exe, I assume?) set up. Dunno the technique behind, perhaps global keyboard hook - I seem to recall that a hotkey override wasn't effective when focus was on a program launched with administrative privileges, that would at least support the keyboard hook theory.