I have no idea what version of the NEC that is or how long it has been around, however I can tell you with certainty that the large majority of homes around here, both existing and new builds, do not have have completely enclosed fixtures in closets.410.16 Luminaires in Clothes Closets.
(A) Luminaire Types Permitted. Only luminaires of the following types shall be permitted in a closet:
(1) Surface-mounted or recessed incandescent or LED luminaires with completely enclosed light sources
A motion sensor bulb usually won't sense the motion with a completely enclosed fixture
But your point is valid, if the fixture is enclosed you would need an external motion detector next to the fixture. Still probably easier to wire in that a door switch and doesn't involved cutting into the door frame.