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It's not so much that women are so appreciative of men's housework that they want to have sex. I think it's that couples in which one partner (usually the woman) is running herself ragged with a career AND a full load of housework is not going to be generally too frazzled for sex. So when a man starts to pull his weight, the woman is going to be correspondingly less frazzled and thus more likely to be in the mood.
I agree with xychro that doing all the housework IS a full-time job. I grew up watcing my mother constantly keeping up on the dusting, mopping, scrubbing, straighening, mowing, repairing, laundry, cooking, dishes, and shopping, and there is no doubt that these tasks take effort and time, and have value. Trying to do all this on top of a full-time job is a nightmare. And that doesn't even include childcare.
(Of course, I disagree with Xychro that housecare and kids are necessarily more rewarding than other endeavors. Raising children can be great, but there other aspects of life that are extremely rewarding too. Also some people are made VERY unhappy by their children. Why do we insist on trying to rank the rewards of child rearing in relations to the rewards of career?)