When were you in college? These days nearly everyone I've seen is paying for interns. Kids from top schools are looking at $15-20k offers from Google and Amazon and at least $10k or so from startups in the Bay and NYC.
The one shop I've seen who didn't pay for interns was in upstate NY and only recruited from a small college nearby. It was hard to take them seriously with just that but when they said they didn't pay, the top students with options just walked away.
Not only are interns doing work but they're being trained and inducted into a company that they have a very high likelihood of returning to. It is a big win for the company if they can try you out at a discounted rate before hiring you full time.