I don't see a big deal with 1 year tenures. Under 1 (3-4 months seems suspicious). I imagine people leave after 1 year if they took a job that wasn't a nice place but they had some incentives requiring them to stay a year (sign on bonuses are typically vested at 1 year; moving assistance also needs to be paid back if an employee leaves within a year).

So ... if a person leaves at the 1 year mark, it was likely they who chose to leave. Given the stories about bad employers in tech and the fact that there are many good employers too these days, I would say good for the moving employee!