George, you bring up a few good points. I'd like to toss out a few of them, and maybe stir up some discussion.
I expect that, strictly speaking, the NEC really doesn't apply "after the plug." Those would be appliance issues, not code issues. Even the famous example of dozens of plugs all cobbled together presents no real hazard, as long as the loads are minor.
The wrong equipment used? Cords subject to damage? Sure- but I can't really see what can be done to protect fools from themselves.
Lights with counterfeit UL lables? Sure, but I don't see what Joe Homeowner can do about that.
Some design issues certainly come up. Even today, I see very few homes built with a deliberate allowance for holiday lighting. A lot of 'jury rigging' would be avoided if only a few receptacles were added where lights are likely to be.
We've seen some awesome displays, some with computer controlled lights synchronised to music. This certainly shows a willingness to put lost of effort into doing displays "right."
Maybe a "standard" home ought to have some receptacles in the eaves, a timer built in, and perhaps a couple "Christie" boxes scattered around the yard.
Yet, I get lots of opposition to the required two outdoor receptacles; even more opposition when I want to put them on dedicated circuits. Receptacles under the eaves are unacceptable when presented as "holiday lights," but embraced when presented as "for ice melting." (The last issue, remember, brings up GFI issues).
I'm not sure what to do about receptacles in the shrubbery. At best, they get grown over and covered with mulch; at worst, they get run into with great gusto by the gardener. It never seems you can mount a "Bell" box well enough, and such boxes corrode away when placed in the ground.