It's the Record Rental Amendment of 1984 which adds to the copyright act of 1976 forbidding the rental of sound recordings by anyone except the copyright holder (i.e. artist or record label).

Movies can be rented because they fall under something called the first sale doctrine which allows anyone who buy a copy of a film to do what they want with it - except of course copy it and resell the copies.

Check out findlaw.com if you even have legal and copyright questions