It's true. For my part, I started (and continued to) answer on a tag with not a lot of questions and answers, so most/some of the time I'd write the only answer. Though I had a professional interest into the tag at the time, I didn't choose it because it was easy to write the single answer on a question.

And that's an example of the system working at its best. You were incented to answer questions nobody else could or would answer. In my experience it doesn't work out that way often.