I suppose this is where soft skills come into play. To be a manager, the most important thing is people management. Of course, the developer / programmer will also need to have the technical skills to look at a project as a large picture and make decisions to lead the same....
IMHO, transitioning from Programmer to Project Manager is not for the faint of heart. And it's not what most Programmers I know want to be when they climb up the corporate ladder. Most of them just want to churn out code for the rest of their lives.
But for a programmer who really wants to be a Manager, I guess he must possess the following qualities:
- Good with People (motivate, reprimand) - Good with Schedule (no scope creep please!) - Good understanding of Domain