Introversion and social anxiety are not the same, nor are they related. Introverts *can* have social anxiety, but so can extraverts.
The difference between an introvert and an extravert is where they get their energy. An introvert re-energizes through solitude. An extravert re-energizes by being with other people.
Either can have social anxiety. Many introverts do not have social anxiety. Barack Obama, Bill Gates, Kim Kardashian, Mahatma Gandhi, Beyonce, Barbara Walters, Mark Zuckerberg, Guy Kawasaki, Jay Z, Marilyn Monroe, Abraham Lincoln, Hilary Clinton, Jimi Hendrix, David Letterman — all introverts. They seem to do fine socially.
Your post is great, but it applies to people with social anxiety, not Introverts in general.