I have no idea how Netflix actually treats its employees, but applying the charity principle leads to other possible interpretations:

- B was chosen arbitrarily to drive the point home and could well mean a D on a school grade scale.

- They don't want to be too hard on fired employees or hurt their future employability (e.g. even "above average" people get fired over there).

I don't know anyone who works at Netflix and I could very well be wrong. Their "performance > effort" policy does however resonate with me.