How does a non-technical manager add value to a team of self-motivated software developers?
By leaving? But, more seriously, a good, non-technical manager can actually be of value to a technical team, if he understands his role, which is it to take care of all the non-technical management - and nothing else.
To illustrate: I once had a manager who used to say "leading programmers is like herding cats", which brilliantly demonstrates that he doesn't understand programmers, leadership and cats. Firstly, thinking that "leading" is similar to "herding" means that you believe your staff are no more than non-thinking cattle. But programmers ARE a bit like cats - they have a mind of their own and see you as their equals - at best. The secret to leading cats - and to any good leadership - is to treat them with genuine respect, so they get to trust you, and never try to hem them in without a very good reason, because they will just walk away. You have to be the sort of person they want to follow.
Most non-technical managers just aren't the kind of person a techie would want to follow, sadly. I suppose at least part of the reason is that in order to be successful in a management career, you have to have a rather conformist mindset; you need to be somebody who likes rules and feels that it is wrong to question them. A technical career, on the other hand, requires you to ask critical questions all the time - you can see how that might make the relationship difficult.