Comment by starky

You are taking the wrong lesson from the article if you think they are saying every (or even most) senior developers should be doing this. You absolutely don't want every senior developer spending their time mentoring/working with junior developers, but having a couple of those people on the team is a force multiplier and benefits the team as a whole. They may not have realized it when they hired him, but he found a useful niche and once the company identified it they should have changed his role to make it official.