Yes and no. The introversion comes in handy when the pen hits the paper, but it's being out in the world and around people that provide the experiences worthy of writing about. You can't be an effective writer in total isolation.
Actually, alahiker28, I am almost completely isolated and consider myself an effective writer-I don't have many friends, do get out to go to the store and some 12 step programs, but my writing continues to be 'acceptable.' I agree your other points!