Of course coaching matters! The point, I believe, is that the relationship between management and creative can be mutually beneficial, with both parties earning considerably more through a partnership than they would on their own.
The fact that developers become much more valuable with a good manager doesn't, in itself, explain why managers are paid more.
For example, let's say a manager without a good developer would be worth 100k of value a year, and a developer without a good manager would produce 100k, but working together, they produce 500k. There is now a surplus.
Now, if it's easy to be a developer and very difficult to be a manager, then it would make sense that the manager would capture most of the surplus, because he or she could always just go and find a new talented developer to work with. The Rolling Stones can find a new manager more easily than a manager can find a new Rolling Stones.
However, ahem, it seems to be the managers constantly bemoaning the difficulty of hiring good developers. Share a bit more of that surplus, and you may find those hiring woes aren't quite so woeful?
