Great article explaining why skilled workers move around so much. It is true, that once you get to a certain point in a job where your value to the company starts to diminish and you need to move on to something new.
I think David is completely right. From my experience, people with families know how to get more down in smaller amounts of time. Maybe it is just more experience or just better time management, but they just get it done one way or another.
Nice compilation of a several Fireworks tutorials and articles.