The NEC does not make any such distinction.
I guess the assumption is that if the raceway is large enough to hold the ungrounded conductors conductors it is large enough to serve as the EGC.
One interesting consequence is that if you have a perfectly compliant raceway EGC but decide to pull a wire EGC anyway, that wire EGC must still satisfy the minimum size requirements.
Thanks for the PDF for grounding of steel raceways.
I particularly like:
The GEMI research project and resulting
software analysis program proved that listed
steel conduit and EMT clearly exceed the
minimum equipment grounding
requirements of the NEC.