How does it work in the market? If possible to generalize, is it a critical point to have a project leader to be a developer himself?
If he is not so much in coding, how can he understand what the rest is really talking about. If he is so much good on programming he might have difficulties on leading probably. If you think about the "good" project leaders you have met, how was this balance?
When the project manager understands the workflow of programming everything is well. The project manager doesn't need to code so he doesn't need to understand it either. All he must understand is what kind of things must be done to complete the project with success.