Tethered by a high-tech leash

MSNBC has a series of articles on “punching the clock in the new economy.” Especially interesting to me is Tethered by a high-tech leash. “[P]eople with Web access at home log in and work an extra 5.9 hours per week on average.” What causes someone to stay constantly connected? Fear of losing their job? A hope that doing so might single them out as an exceptional employee and get them the bonus, raise, promotion they desire?