I just found this article while searching for other things. It gives considerable evidence that exclusively breastfeeding moms who are co-sleeping get about 40 more minutes of sleep a day. http://www.infantrisk.com/content/nighttime-breastfeeding-and-depression
Apparently there's been a trend to tell moms at risk of depression (or who are depressed) not to breastfeed at night, but to formula feed to get them more sleep. It seems that's a false assumption. I'm really glad no one suggested that to me when I had postpartum depression!
I guess the bottom line is that parents of young infants are indeed sleep deprived and all you can do is minimize it.