I believe I have discovered what it going on. I asked about this weird behaviour in the Excel developers forum over at MSDN and was told that Office 2010 can be downloaded as a try and then buy package from the MS website. Users are encouraged to use the new MS Click To Run (CTR) technology that installs Office 2010 in a virtual environment so that it can be installed side-by-side with an existing (earlier) version of Office. In fact, the majority of users who download the try / buy version will likely install using CTR as MS have burried the details of how to install it as a regular msi based installation.
On a CTR install of Office 2010, the following registry key is NOT created:
SOFTWARE\Microsoft\Office\14.0\Excel\InstallRoot\Path
Instead, we are supposed to check if there is a virtual installation by looking for the following key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\14.0\Common\InstallRoot\Virtual\VirtualExcel
I imagine that it will be the following for Office 2012:
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\15.0\Common\InstallRoot\Virtual\VirtualExcel
BTW: For Outlook, the key is:
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\14.0\Common\InstallRoot\Virtual\VirtualOutlook
I imagine the same goes for the other components of Office like Word and PP.
Hopefully you'll be able to address this in a future release of AI as it seems like this will be a popular way of installing Office in the future.
The folks at MSDN pointed me to this link about detecting if Outlook was installed virtually:
http://msdn.microsoft.com/en-us/library/ff522355.aspx
To check whether Outlook was delivered by Click-to-Run on a client computer
Verify whether the VirtualOutlook key exists in the following location in the Windows registry:
HKEY_LOCAL_MACHINE\Software\Microsoft\Office\14.0\Common\InstallRoot\Virtual\VirtualOutlook
The VirtualOutlook key is a REG_SZ value that contains the culture tag of the installed product language, such as "en-us".