I can't comment on online courses, but in general there is a HUGE difference between people who get As and people who get 100% on every single assignment. Never making a single error is an amazing feat.
I personally have only scored straight-100%s in a single course (Python programming), and that was only because I was relatively an expert in the material before the course began.
If you are getting 100's on everything it means you are gaming the spirit of the learning, overfitting the memory. Plop that guy in front of a computer with specs and a deadline and you will learn why grades are not an indicator of success.
Well, the only two people I personally know who would get all 100s are Peter Norvig and Sebastian Thrun, and I personally wouldn't mind hiring them!
Of course, in reality, Peter Norvig and Sebastian Thrun are working on projects that have long time horizons, e.g. self-driving cars and search. So perhaps you're still correct: The people you would hire to bang out code to meet a short deadline are probably different from the people you would want to work on your long-term technology bets.
In general, I disagree that knowing a topic incredibly well is necessarily overfitting. Deep knowledge can only aid new insights. You often hear about mathematicians and physicists who think by inhabiting their own mental world, composed of insights that they hold so deeply that they are _intuitive_.