The extensions are there but if you want the path where the application is installed you have to look elsewhere.

An example

On my system: HK_CURRENT_USER\Software\Adobe\Acrobat Reader\7.0\InstallPath

Value: "C:\Program Files\Adobe\Acrobat 7.0\Reader"

If this lookup fails look at HKEY_LOCAL_MACHINE\software\companyname\product. I think this is in general the lookup strategy, i.e. first check HKCU if that fails check HKLM. Like I said it depends on the user logged on. I also recall (on the top of my head) that the registry differs (slightly) between different Windows flavours.

See also Windows registry information for advanced users.

HTH