The Launcher is a control panel. When a control panel is open, its resources are in use. Since the version information is kept in a version ('vers') resource in the control panel's resource fork, the Finder is unable to access this information. This why "n/a" (not available) is displayed in the version section of the Get Info window.
If you want to obtain the version of a control panel, close the control panel and then close and re-open the folder that contains the control panel, which is typically the Control Panels folder within the System Folder.
By closing and re-opening that folder, the cached Finder information is updated.
The Finder caches many resources that are displayed in Get Info window such as custom icons and 'vers' resources to increase performance.