Why do you think it's "clear" that the business owns the contacts and relationships? Contacts and relationships form the basis of a salesman's job, much as language and API expertise are the basis of a programmer's job. You may invest considerably in a programmer's training, only to watch him leave for a competitor, but you will have a difficult time claiming ownership of his knowledge and experience.

I think the lesson is that, from a business perspective, you need to guard access to key contacts and companies where possible, if the likely departure of an employee who knows them will cause the business undue hardship. How else would you propose to structure a job where the employee forfeits relationships upon separation? (And how would you get any decent salesperson to accept such a job?)