> why not use the same syntax as can be used for manifest.mf : for storing this ? 

The file this is being stored in has a data store that is an xml file. It was previously used to store filesets, and, in teh current implementation, a user can customize responses to add both filesets AND/OR jboss-modules entries. It's possible in the future we allow even more entry types to be added to the list. 

With the requirement of backwards compat, an existing xml data store, and user flexibility (not locking them into using ONLY jboss-modules entries), I upgraded the format of the backing xml (backwards-compatible) to add the jboss modules entry as a new type. 

I will double-check whether the backing instance (xml datastore) stores it as 'main' or blank.