I dont' believe that at all. I love sex and initiate it probably more often than my husband does.
Maybe women, after having children, get tired and feel unappreciated and that turns them off but when rested and happy we have just as many urges as men do.
After my kids were born there was a time when I didn't want it at all but that's with being up all night with babies and never sleeping more than 2 hours at a time. Once they got a bit bigger it all came back. Now, I'm the one on this website and he isn't. The longer we're together the better our sex life is. The more confortable you are with your partner the more willing you are to try different things and the more you trust them the more willing you are to communicate your wants/needs/desires.
Maybe if the wife (wives) you're talking about got more appreciation for the cooking, cleaning, laundry, grocery shopping and other boring never ending jobs she (they) do and even a little help with them they'd have more energy for sex and be more passionate in general. There have been times that I've gone out for the day on a weekend and get home and he's cleaned the whole house top to bottom and I'll tell you when that's not hanging over my head the sex at night is amazing 'cause I'm not overwelmed with what I have to do the next day and I find myself more attracted to him because of the help.
(I'm sure some out there do help and show appreciatiion....obviously I'm talking in very general terms)
Just saying