> Anecdotally accurate? Check. Has a reasonable model? Check.

To the former part: horoscopes are also anecdotally accurate, and hence the comparison. Good horoscopes and other forms of cold reading are specifically designed to offer people given situations they can relate to: "sometimes you feel like you're the life and soul of the party, but it's interesting, because you represent a contradiction - there are times when really you just want to be alone" (source: I just made that up)... Compare and contrast to: "As an INTP, your primary mode of living is focused internally, where you deal with things rationally and logically. Your secondary mode is external, where you take things in primarily via your intuition." (source: first line of first result for INTP on Google) You mean ... INTPs are sometimes rational and logic, and sometimes intuitive? ;-)

To the latter part: the model is a big part of the problem. It polarizes personality traits that are necessarily context-dependent, mood-influenced, and exist on a scale in to binary Yes/No. If you're not Introverted, you're Extraverted. Not: "you're in the middle, and occasionally tend to one or the other" - simply: "you are x".