It is probably also industry (and city) dependent, I have found at my job in a midsized city that there are a number of probably life long friends within my company. Also, because it is one of the largest tech employers in the area, many of the intelligent people who want to stay in city (due to family and growing up in the area) want to and do spend their entire career there. We also have pretty reasonable career paths for people who want to only work 40 hours a week and for people who want to work more.