EXPORTing subprocedures

OK, here is something I have never quite understood. Can anyone explain why subprocedures within a Linear Main *MODULE have to be EXPORTed - even when only referenced within the same *MODULE?

Example: A single source member follows, (please be gentle with my coding.) CRTBNDRPG used with this particular example.
**Free
// Linear Main *MODULE with subprocedure
// Subprocedure MSG requires EXPORT keyword - why???
Ctl-Opt DftActGrp(*No) Main(MainProc);
  Dcl-PR MainProc ExtPgm('PGM2_PROC1');
  End-PR;
Dcl-Proc MainProc;
  Dcl-PI MainProc;
  End-PI;
  Dcl-PR Msg;
  End-PR;
  Dcl-S UserId Char(10) Inz(*USER);
  Dsply 'In MainProc' UserId;
  Msg();
  Return;
End-Proc;

Dcl-Proc Msg Export;
  Dcl-PI Msg;
  End-PI;
  Dcl-S UserId Char(10) Inz(*USER);
  Dsply 'In Msg Proc' UserId;
  Return;
End-Proc;

If I rewrite the above as a Cycle Main *MODULE, the EXPORT keyword is not required on the subprocedure. The RPG Reference states:
"If the EXPORT keyword is not specified, the procedure can only be called from within the module."
So why is EXPORT needed in the above example? (If it is removed, a bind error occurs.)

Thx for any insight.
Brian.