That happened AFTER the provisions of Islamic law which exempted the indigent, the invalids and the old were discarded.
By the way, I guess I found your source -very "reliable":
http://en.wikipedia.org/wiki/Shelomo_Dov_Goitein
PS - Muslims not paying Zakat is akin to stealing in Islamic law. AND AGAIN, when Muslims risk their lives in the army to protect you, it makes sense to pay -provided that you can. When ONE non-muslim joins the army, the army becomes national, and the Jizyah is waived.
Again, Zakat is a percentage, which can reach 100x folds that of Jizyah, which is not.