I do see the value in interpersonal and teaching skills. The best developers have them and are interested in helping others. In my experience, though, programmers tend to be introverted. One definition of introversion is that interacting with people drains them of energy. So being a teacher is harder work than just writing code and probably pays less money. That's why I said especially that it needs to be explicitly paid for in this scenario. Otherwise the developers will go elsewhere.

A similar problem exists in consulting companies. It's hard to find people who are great at programming, great at managing people, great at doing sales, and great at running the business. The rare person can do it all, but you can't hire for it. Everyone like that is running their own business.

So you end up with a split between the technical part of the team and non-technical managers. In this case it's usually the non-technical managers who make all the money :-)