The emphasis on humor in Mozart and Beethoven is interesting, particularly since it seems almost absent in the later Sonatas. I remember hearing Martha Argerich note that it's present in early Beethoven, and then disappears in Chopin and Liszt, and then reappears a bit in Ravel, but truly with the Russians. I would be interested in whether Brendel distinguishes between the ironic humor (Mediant vs Dominant) and any other types.