You can see this file by right-clicking the program and choosing Show Package Contents and then opening the Contents folder. High-resolution mode support and other features of a program (such as readable document types and system version requirements) are stored in a property list file called ist that is located within the application package itself. Opening the ist file for each application shows that each does contain the appropriate key and value for triggering high-resolution mode (click for larger view). If you get information on the program in the Finder (select it and press Command-I), you will see the Open in Low Resolution setting is grayed out and checked, which is the default behavior for programs that do not support Retina displays. It appears the system simply is not recognizing the new high-resolution capabilities of Office. In some cases one or two of the Office programs appear to run in Retina mode, while the others do not.
Yesterday Microsoft released an update for Office 2011 for Mac which added high-resolution support for Apple's Retina Display however, after applying the update a number of people are finding the Office programs still open in low-resolution mode.