It's very common in many industries. A company will take an inexperienced person, likely in college, and they will work at that company for 8-10 weeks over the summer. They learn the ropes, do menial jobs like filing, running errands, answering the phone, getting coffee, etc. It's a good way for a young, inexperienced person to learn about an industry or company and see if they want to pursue that as a career. And companies can develop a talent pool to choose from and bring in those who can be an asset to that company.
But the most important part of it all is building relationships and networking. You cannot ever over estimate the value of networking and building contacts in any industry. My niece is doing an unpaid internship in the clothing and fashion industry in NY this summer. She doesn't care that she won't get paid for 8 weeks, but the experience and contact list she will build over that time period will be very valuable in 2 years when she graduates from college. It's the way it's done in many industries and is one of the best ways to get your foot in the door.