People often post links within their answers and comments. When those links contribute to the discussion, the profile associated with the site hosting the link could earn some reputation.
For example, I could earn some reputation :) since my website is cited several times on stackoverflow.com, see http://stackoverflow.com/search?q=www.monperrus.net
With proper stabilization mechanisms (site verification, no self-links, etc.), this could be a way to build a stackoverflow-based internet-wide Q&A reputation.