NYC Chancellor won't grade himself

If this is how the Chancellor evaluates himself, why is he grading schools and teachers on a curve that ends with letter grades, or their equivalent? From an interview with Anna Phillips:

Q. If you were to rate yourself, give yourself a grade for your first year as chancellor, whether it’s an A through F or a 1 to 10, what would you give yourself and why?

A. And my response, and this is my honest response, is I don’t give myself a grade. I don’t really focus on that. To me it’s the satisfaction of what I see when I go to schools and when I interact with students. You know me, you guys have been trailing me for a while. I just love being in the schools, I love being with the students, hearing what they have to say, meeting them, watching them learn, watching them answer questions, and my quote unquote grade is derived by the type of interaction I have with them and they have with me.

For the record, I do not think the Chancellor should have the very complex aspects of his job reduced to a number or letter; neither should teachers nor students for that matter.