Why do cats love to curl up near the fire or nap in the sun?

I have wondered about this for a little while - I mean, cats are already covered with fur from head to tail, and yet they bask in warmth any chance that comes available. Sometimes the shower will be going in my house and my cat Mocha will just sit there beside the tub while the bathroom fills with steam, acting as though she is in a 68 degree room and perfectly comfortable. But, it does come in handy when I want her as a snuggle buddy. If I am watching a movie or taking a nap, she curls up faithfully on top of the thick comforter and loves it. Perhaps she does get hot but slips away and sips an iced Margarita while I don't know it. :)

Well, time for bed. I'll go get Mocha - she's sleeping by the fire. :)