If they do think about sex a lot, meaning the older ones, then the kind of sex THEY think about is much different then the kind WE think about. They think about their man being romantic, lighting candles, maybe a bath and a massage, telling them how beautiful they are. Then probably mish and maybe doggie and they MIGHT reward you with a BJ. Then cuddling when it's over. That's fine and dandy occasionally, but not all the time, every time. WE want variety. WE want role playing. WE want dirty, taboo, multiple, unexpected etc. Basically what we all enjoy in watching porn. While we won't get most of what we see, we still want a lot more than what their idea of sex is. So while some men still get it from their wives on a semi regular basis, can it not be the same every time for the last 20-30 years?
Helping them with the kids, chores etc should be expected. Cooperation is always important. But in my experience, it just means they get more time to sleep, not exactly what we are expecting. I for one would give up sleep for sex. I think for them it's the exact opposite.