This behavior is by design. Windows Desktop Search installs a MAPI Protocol Handler. This handler is responsible for indexing data in earlier versions of Outlook. Outlook 2010 and Outlook 2013 now include some of that indexing and search functionality in the program. Because the new functionality is built into Outlook, the original Windows Search indexing components and addin are disabled in Outlook 2010 and Outlook 2013, but not removed. This ensures that earlier Outlook versions can be indexed correctly if Outlook 2010 or Outlook 2013 are uninstalled.