I think the lampholder verses luminaire issue may be more of a local building code issue than NEC.
As I recall, possibly something about lampholders being okay for inhabitable areas like attics, basements, garages and crawl spaces, but not so much for habitable areas.
This may possibly have been due to home buyers purchasing the "builder homes" during the housing boom, equipped with all the cheapest crap the local home centers had to offer, such as vanities and cabinets, etc... and having the venerable keyless installed everywhere a light fixture was required just to get the final electrical and CO signed off, then having them remain in place for years after the sale.
