Mike, I THINK the rear rotors are just held on by the wheel. The circle in the middle of the disk with the two notches is actually the end of the axle and the rotor fits around it. Now that you have the wheel and calipers off just give the disk a couple of whacks with a dead blow or rubber mallet and that should loosen it up enough for you to take it off.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless