It certainly is not. This has been a necessary consideration from the early centuries of the papacy, and certainly even more so in the past 20 years as digital communication has put practically every word of the Pope before the eyes of every Catholic and, of course, non-Catholics as well.
It is simply not true--- and never has been true --- that every word from the mouth of the Pope (or every sentence from his text program) comprises Catholic Doctrine. The Holy See itself lists a number of categories of Papal documents (FOUND HERE), with different levels of authority:
Motu Propriobut even these categories don't begin to account for distinctions within each kind of document.Apostolic Constitution Encyclical
Apostolic Letter
Apostolic Exhortation
Common Declaration
Homily
Audience
Discourse
Message
Pope Benedict XVI was, I think, the first pope to write and publish books during his pontificate which were non-Magisterial. In the preface of "Jesus of Nazareth: from the Baptism in the Jordan to the Transfiguration" he wrote:
It goes without saying that this book is in no way an exercise of the magisterium, but is solely an expression of my personal search for the face of the Lord (cf. Ps 27:8). Everyone is free, then, to contradict me. I would only ask my readers for that initial goodwill without which there can be no understanding.
You can wish that no pope should ever say or write anything sub-Magisterial ("prudential judgment" or "theological opinion") but that has never been, and I daresay will never be, the case.
It's no use to swing back and forth between two false extremes, papal maximalism ("He's an all-purpose oracle") and papal minimalism ("He's just a guy with an opinion.")
There's a of of gradations in between.
I wish more people were aware of that.
Pope Francis: "Im constantly making statements, giving homilies. Thats magisterium. Thats what I think, not what the media say that I think. Check it out; its very clear. The Joy of the Gospel is very clear."
http://americamagazine.org/issue/we-must-reach-out
mag·is·te·ri·um ˌmajəˈstirēəm/ noun the teaching authority of the Roman Catholic Church, especially as exercised by bishops or the pope. the official and authoritative teaching of the Roman Catholic Church.