Well, at the very least, I'd like to see how they decide. Are there key words that they use? Is it sentence structure? If there's no good answer, then I'll agree with you. (and I'm already tempted to agree with you, though I'm still curious.)
I tried several different writing samples, too. I, T, and J were fairly consistent, but N/S was all over the map, apparently dependent upon the topic of the writing. The N score here came from a several-paragraph answer on another forum to a question I really enjoyed addressing (i.e. reflects my topical preference).