Shyness vs. introversion

Interview with Jonathan Rauch, who wrote a great essay about introverts. (via kottke) Mentioned in the interview but still unclear to me is the difference between shyness and introversion. Says Rauch:

"To me, shyness implies a real reluctance to be socially aggressive or assertive. It's very difficult for shy people to put themselves out there if they need to. For introverts, it's never easy to do, but it's more a matter of reluctance to expend the energy, because it tires us out."

My view from things I've read on the subject is that introversion is a personality type while shyness is more of an undesirable trait. Shyness is something that can be changed, but introversion is something fundamental about your personality that is probably impossible to change. You can be an introvert and not shy, I suppose. However, it seems like there's a close connection between the two. I can't think of a person being shy who is not an introvert. To me, it seems introversion lays the groundwork for shyness.

Further on, Rauch says:

"I think that's probably a core introvert characteristic that you and I have in common and which can probably be distinguished from shyness per se—that small talk takes conscious effort and is very hard work. There's nothing small about small talk if you're an introvert. But we're good at big talk."

I think the point he's trying to make is that introverts don't have a hard time expressing opinions if it's something they're interested in, but they do have a hard time coming up with social banter. But isn't that exactly why people who are introverts become shy? They have a tough time engaging with people because the small talk needed to get a conversation started doesn't come naturally to them. Which leads to frustration and a reluctance to want to put themselves out there again. It's like shyness is a pitfall of introversion that you have to work to avoid.