Interestingly, the dogs here that sleep in/on the owners beds are all of one type - sighthounds, Whipps, Greys, Salukis.
Whippets used to be called 'bedwarmers' as they were put into the kids beds to keep them (the children) warm (and also stop the dog freezing).
Whipps and Greyhounds lack underfur and fat to keep them warm, so you either need a warm house, pyjamas or your bed to keep them warm at nights. From what I've seen on Whippet discussions, most sleep on or in their owners beds or curled-up in front of a fire.
Neither can these dogs sleep on hard surfaces and have a natural desire to be high-up - it's part of their hunting instincts, so they constantly want to be on the sofa/chair, on the bed.
It's the nature of the beast....