Hi Bob
The reason ranges are not listed in 240.4 is because you are still require to protect the branch circuit conductors at their ampacity rating. If you run #8 60C conductors to a range you must protect them with a 40 amp overcurrent device. The conductors listed in 240.4(G) are generally allowed to be protected by branch circuit overcurrent devices exceeding their rating.
I don't know how the demand factor for ranges ever came about or any of the demand factors for dwelling units for that matter. I do know that the seem to work. I have wired many ranges to 40 amp branch circuits and have never had a call back because of a tripping breaker. There are also probably over a million apartments in this country supplied with 50 or 60 amp feeders that have 12kw ranges in them.
My guess is the NEC looks at ranges similarly to the way it does welders. The full load nameplate rating will never be on the branch circuit very long so running full sized branch circuit is unnecessary. The reduced branch circuit can easily handle carrying more than its rating for short periods of time.
Curt
