Bob,
Part of the answer to your question will also come from local ordinance. I infer from your question that the closet luminaire with the bare bulb is installed in an existing dwelling. The NEC only covers new wiring, and doesn't directly apply.
In my part of the country, I'll see the bare bulb fixture installed in closets of homes built in the Sixties and before. Local ordinance requires that any such closet light be at minimum replaced with a fish bowl enclosed surface mounted luminaire (in most cases, the luminaire you saw at the orange box is perfect). However, the requirement to replace the bare bulb unit is only required when the service center is replaced or increased in ampacity.
Bottom line. . .I'm certain I'll be installing that pullchain fish bowl, a few at a time, until I die.
