Did you miss adjective "UnPaid" in his sentence with respect to the types of internships being discussed? There are paid internships too.
However, IANAL, but from what I recall there are no legal differentiations between "paid" and "unpaid" internships. Under the law they're both the same thing - which means there's nothing stopping employers from making all their internships unpaid.
In seeking the unattainable, simplicity only gets in the way. -- Epigrams in Programming, ACM SIGPLAN Sept. 1982