I have been with my employer for 17 years (program manager in county government) and my DH has been with his employer for 20 years (lead operating engineer in a power plant). We would consider ourselves "settled" in our careers. One of the major reasons we are settled is because we both have traditional pensions, and are vested.
I think one of the reasons that the tides have turned, and that people don't stay with the same employer forever anymore, is that few companies offer pensions. With portable pensions, and/or 401Ks, becoming the norm, there is really no incentive to be loyal to one employer forever. Many employers don't seem to very loyal to their employees either. So, if I was in a situation like that, I likely would move around and make the most money I could make.