If you are a clean person and shower every day, wear clean underwear everyday, they don't need washing every week. I don't wash jeans unless they get spilled on, or winter salt stains. As long as they don't smell like ass and they look clean, why bother, washing jeans, it's what makes them get old.
But if you are a pig and never clean yourself or your underwear, your jeans will stink after one wearing, but I don't think that guy cares if he smells like ass. We all know somebody like that, if you don't, he is probably you. Maybe that's why women are compelled to wash after every wearing, afraid of Bears.
I had the same conversation about wearing the same shoes everyday, same thing shower everyday, wear clean socks, no problem. I know this will not pertain to certain posters that own as many shoes as women.