I had recently a weird thing. I did a custom install for Office 2010, removing all module apart from Outlook. After applying Service Pack 2, Tada, all Office Applications were listed in the Office folder!!!!
To make sure this does not happen, we need a Microsoft KB that has been recently updated and the explanation of how to integrate it in Office 2010 sources:
To sum up, extract files from KB, and copy them in your UPDATE folder in Office 2010 sources, and voila!