It was probably mentioned in the earlier discussions, but I believe the "two humps" pattern can easily be explained by bad teaching. If it hapens in the whole profession, maybe no one has yet discovered a good way to teach it, because most of the people who understand the topic were autodidacts.

Bad teaching? There's an even simpler explanation (at least regarding programming): autodidacts with previous experience versus regular students without previous experience. The fact that the teaching is often geared towards the students with previous experience and suffers from a major tone of "Why don't you know this already?" throughout the first year or two of undergrad doesn't help a bit.