http://www.msnbc.msn.com/id/21091112/ns/health-sleep/t/men-sleep-better-beside-mate-women-worse/
Anecdotally and from personal experience (particularly from my younger days of doing shit like taking 3 day wilderness treks with groups and then sleeping in big cabins or tents) I would suspect a lot of it has to do with the propensity of one gender, in particular, to snore louder and more than the other.
And I don't mean women.