During IBM's "buyout's" in 1991-1993, many employees had to sign an agreement not to work for the competition, as a condition for receiving certain types of benefits. I was one who fell into this category. My "buyout contract" also specifies that I must have IBM's approval on any job that I take. The penalty is repaying the severance benefits and loosing certain aspects of the sweetened early retirement package I must take in 2001.
Companies CANNOT afford to train people who may be future competitors. "On the job training" is being considered a performance reward in many firms. There are so many people in the job market now competing for so few jobs that many employers prefer hiring people with the skill rather than paying for training. There are no "jobs for life" anymore at any company.
What I find interesting is that the public education system in Iowa has similar concerns. For years, they have provided excellent public schools only to find their "best and brightest" moving to other states. All my in-laws were educated in Iowa in the '50's and '60's. Not one is still living there. Most of their friends, many "professionals," live in other states.