Interesting, I wonder if this is a new development (can't find that in my 2005 NEC codebook). I did run across something else, though, 200.21B2 states that the total load on a single 15-amp receptacle cannot exceed 12 amps, which might also apply.
I guess I'm going to have to go back and re-read the whole section. This concludes the thread-jack. We now return you to the regular discussion.
Hair dryer, slow cooker, electric space heater, etc are all demand loads and can use 100% of the rated ampacity.
Edit: Source: Article 100 of NEC