I think the argument against unpaid internships is not so much that they don't provide value, but that they're only open to people who can afford to do an unpaid internship.
I'm in agreement with you on that - we pay all of our interns at The Muse. The posting referred to above is a way of recruiting people who are interested in contributing 1-4 mentoring posts per month, so very low commitment nights-and-weekends type thing.