I love it when they do that. Reeses is just beautiful, especially when she poses so prettily. My Mom's cat (being the regal lady that she is) always sits like that.
Unfortunately my teenage boys have not learned any such delicate manners yet.
I wonder if this is a calico thing. Frankies favorite place to lay is on the kitchen rug, on her side, with both front and back paws crossed over eachother.