Course completion is a valid goal, and an important number. The point that I'm making is that a 5% completion rate is still a success, when multiplied by the massive number of people enrolling.
For an individual, if you watched the first three videos of linear algebra and stopped, you didn't learn the subject and can't honestly claim you took the course. If you finished it past-deadline but did all the exercises, you're probably ready to take the next course.
Udacity and Coursera are a step forward. Perfect? Far from it. Ready to replace Stanford? No, not even close. Is the world better with them than it would be without them? Absolutely.
Education, in technology, is there mainly to give you a root set and confidence. If you actually want to get into machine learning, you have to start reading papers anyway. That goes whether you're a graduate student or a DIYer who's been in industry for almost a decade like me.