the origin of commentary writing

I've begun reviewing Ruth A. Clement and Daniel R. Schwartz's edited volume, Text, Thought, and Practice in Qumran and Early Christianity (Studies on the Texts of the Desert of Judah 84; Leiden and Boston: Brill, 2009). The first essay is Markus Bockmuehl's, "The Dead Sea Scrolls and the Origins of Biblical Commentary" (3–29), a thus-far interesting examination of pesharim at Qumran and their relation to Greco-Roman commentary practices. In a footnote Bockmuehl drops a rather interesting suggestion, which I thought I'd throw up against the InterWeb and see if it stuck:

Prof. Horbury suggests to me that the learned nature of Alexandrian poetry may itself have encouraged a commentary tradition, and that recondite biblical texts that explicitly required interpretation (e.g., Zechariah, Daniel) would have fostered an analogous Jewish interest. (9, ftn 19)