Doesn't she receive that percentage in the form of food, clothes, and housing?
I've always thought marriage was 50/50 with no one person having more control or more access to anything than the other. If he spends "X" amount of dollars on restoring a new hot rod in the garage or on fishing poles or whatever, she can spend that same "X" amount on her new hobbies, new clothes, whatever. In the same way, she needs to make sure his needs are being taken care of and that the money isn't just going to the kids or what she thinks is needed around the house.
Giving a woman an actual handout of money makes her seem like an employee or something worse, not a life partner.