Or maybe it means that women get so much out of the sleeping part of "sleeping together" and are looking for a way to express that sex isn't all it's about.

Hmmm... Interesting point! I did know a lot of friends in college that would sleep in the same bed as their boyfriend even when sex was in the plans (like my roomate and her boyfriend who both told me nothing would happen so I didn't have to find another place to sleep.) So I would bet that there is something more going on emotionally when you share a bed.