Yes there is a double standard. But let's face it. Women are just more pleasing to the eye than men. There's less hair, and less wrinkley skin. (Ewww)
Men tolerate guy on guy action far less than women tolerate girl on girl action. Most women have a bit of lesbian tendencies in them anyway. At least that's what I've encountered in the past from talking to different people.
YMMV,
Jen