I think this is spot on! Speaking from my own personal experiences, I'm very introverted and I believe working in customer service has helped me with social skills and now I won't shut up! HahaI think there is a natural predisposition for an individual to lean one way or another.
A combination of innate genetic proclivities along with social environments that either foster it and just make it grow or inhibit it and have it build up as a means to survive the less natural conditions.
Overall I find that it is greatly beneficial for an individual who is overly extroverted or introverted to practice the opposite every so often.