We are getting into an area about the difference between safe and legal. 240.4(D) was put there for safety and it is really there because the NFPA people know 14/12/10 is used on circuits where the loads are likely to be cord and plug connected.
The assumption is that the installer will not know what the user will actually plug in. People will keep plugging in things until the breaker trips and then unplug the clock. They build the 80% into the maximum breaker size. That still does not change the requirement that hard wired continuous loads are still limited to 80% of the breaker size, as KJay points out.
Whether the NFPA should put the same kind of exemptions for lighting loads into the code that they have for motors is conjecture but you still have a few weeks to write a proposal and see what they say.
