Living in a "right to work" state, I don't see a lot of employment contracts like the ones described in this article. The closest thing I've experienced is a 90 probationary period. During the first 90 days of employment, an employer can fire a new hire for any reason at all. Most employers use that time to evaluate the new employee, however, not to find reasons to terminate him or her.
I've seen these breach of contract cases more often in upper management and skilled labor positions. These employees or managers were hired for their specific skillsets, and it makes sense for companies to spell out exactly what's expected of them in a legal contract. If I were the CEO of a company, I would want the ability to fire an underproducing salesman for his lack of effort.