The NEC has to be adopted by a city or state to be in effect. for the federal gov't, they fall under OSHA,
Mainly correct. Government adoption is coercive forcing people and companies to use the mandated standard. OSHA is the federal mandate. In Indiana 675-IAC-17 (Indiana Administrative Code) is the state mandate. Local authorities often have their own mandates. People and corporations may also mandate to those they have authority over. The biggest stick wins.
and the general duty clause would mean the 11 NEC is effective Jan 1, 2011 ( I may be wrong and it may be the effective date published in the NEC)
Not correct.
The general duty clause does not mandate adoption dates of any type or any time. Specific sections such as 1910.6 exist when standards and adoptions are mandated.
For the interpretive path you are following for the general duty clause the summary would be:
A) Failure to adopt a standard can be considered negligence.
B) Adopting a standard that is grossly obsolete can be considered negligence.
C) Adopting a standard that is not widely accepted, tested, and approved can be considered negligence.
In short, a state may elect to write its own custom electrical code, updated regularly, reviewed by electrical professionals regularly; and by doing so they would never have to adopt the NEC at all.
As a better example of this consider the NFPA79. This standard covers industrial machinery but is not mandated by any government authority that I am aware of. OSHAs general duty clause can be applied to an industrial site. If you fail A,B, or C above then you open your company up to OSHA actions. If you adopt NFPA79 then you close that door. Or you can write your own standard or adopt a different standard.