Inky, the cat that I had when I was a little girl, LOVED to do that, too. We always thought it was either because it was nice and warm on top of the fridge or because he liked being able to look down on his kingdom!
Cats LOVE to be up high and be able to look at everything. I used to, used is the key word, be able to keep my flowers in a vase up there. It's really funny too, because Munchkin cats seem to have a reputation for not being able to jump, but the ones I always catch napping up there are Munchkins..LOL