Why can't I install Xcode 4.4 on Mountain Lion? When I try to download the Xcode 4.4 update I'm presented with this error:

Xcode can’t be installed on “Mac HD” because the version of OS X is too new.


But the change log says that the update is for Lion and Mountain Lion.
You can manually clear the store where the App Store saves the downloads before completion:


Quit the App Store app
Open Terminal.app (search with Spotlight)
rm -r /private/var/folders/*/*/*/com.apple.appstore

This step is the removal part...
Restart the App store.app