1966, the folks at NASA wanted to nestle pilots' tushies. Pilots worked hard, they risked their lives, they deserved a happy backside. Some strategic nestling would also protect the tush in a crash or during sudden vibrations.
I'd probably never use an electric blanket—I've just heard too many horror stories that include elements like burn marks and houses transformed to ash. But a water cooled/heated mattress? That sounds downright brilliant.