I think of written music as a road map. It is useful to show you how to get from here to there, but when you are actually driving you should have your eyes on the road.

It really doesn't matter if the tune is learned by ear or from written music. All that's important is how it gets played. I've played with mechanical readers and readers who get it and play it right. I've played with mechanical ear-learners and with beautifully expressive ear-learners.

Memorization doesn't enter into it -- someone who learns by ear and wants to play the tune has to memorize it. Someone who learns from written music can either memorize it or not. In my experience, most note-learners who memorize the tunes play them more naturally in group settings, but this isn't always true.

Improvisation is different from both ear-learning and note-learning, although it can be used in conjunction with either.