Yes, I was about to make the purring point myself. While it makes sense to me that some of the seeming need for affection is just mixing scents, three of my four cats prefer to hop onto me, curl up and go to sleep, wherever I am, if I sit down. And Snowball, who gives me headbutts and nuzzles my ears as her way of marking me, really purrs up a storm as she is doing so. She could just mark silently, but she is showing her contentment as well. Moreover, if I stop petting her, well after I have her scent on me, she will rub her head on my hand to ask for more. Or she will stand up and rub her face on my cheek again. That's about as clear a "desire" to be petted as I have seen. I don't attribute it to emotional attachment, though. I think it just feels so darn good to them, they want more!
I should add that I have read some of the love for petting may come from the fact their mothers licked them when they were kittens, so it is comforting to them. Also probably stimulates their appetite.