I'm sure Kisabre's cat just really loves the attention.
I just thought of another thing. In very young kittens, when the mother grooms them they'll flip over so she can lick them to go pee and poo. Young kittens will sort of get in this position when people are fostering them too.
Could some of the turning over be a left over behavior from that?
I only wonder this because Tomas will roll over in my lap and do the baby kitten position...kitty privates up... I'm not his mother cat and he's 8 months old, lazy little bum.
I'm probably putting too much thought into this, most people just pet their cats and think nothing of it.
Oh, and to the poster that suggested it was fleas... If you were covered in fur and didn't have hands to scratch those naturally itchy spots, you'd get itchy too. And if you had a nice owner (read slave) content to sit there in scratch you, you'd take advantage of it.