Dueling Doctrine

I hesitate to post anything about doctrinal questions here as it has gotten me in trouble in the past, but this one is an honest question so maybe I can get away with it.

What is the substantive difference between the Catholic Doctrine of the Infalability of the Pope and the Mormon Doctrine that The Prophet will never lead us astray?

We often poke fun at the Catholic Doctrine because so many popes through history were clearly corrupt, but a close reading of the catholic doctrine will point out that it does not refer to his personal character or dealings in secular matter only that when speaking on matters of doctrine he is "preserved from error".

Mormons likewise believe that the prophets are humans and suffer from all the frailties of humans, but the phrase "The Prophet will never lead us astray" is uttered regularly as if it were doctrine and that seems to be the same essential sentiment.

I'm also unclear on the scriptural basis for the assertion. I can trace it to a talk given by then Elder Ezra Taft Benson who cites Wilford Woodruf's talk defending the first official declaration. There is also an unsourced quote wandering around, but one never knows if unsourced quotes were every really said at all.

I'm personally bothered because I thought that personal revelation was the hallmark of our religion, not obeysence to any scripture living or ancient. It is by personal revelation that we know the Bible, the Book of Mormon, and all the other scriptures to be true. It is by personal revelation that we know that the prophets are in fact prophets of God.

Why then are we discouraged from seeking personal revelation on matters once the prophet has spoken on them? I know some will say that we are encouraged to get personal confirmation, but really it's only confirmation we are encouraged to seek. We are told to pray to know that it is true, not to pray to know if it is true.

I'll stop there for now. So tell me, what am I missing?