I worked on a 89 Corvette front brake job this weekend. Rotors tend to stick to the hub with heat/moisture/rust. Take a scrap of wood, place it flat against the rotor wear area, and give it a medium whack with a hammer, now rotate and do it again and again until you break up that thin layer of rust that is bonding it to the hub. Viola! it'll fall off after a few whacks.

good luck