Written in light of the node Why don't men shave? which had waaaay too many write-ups to justify me adding another, therefore this write-up is being placed here.

The theory that this write-up is operating on:
Women shave their legs/armpits in order to look younger, child-like, and more desirable to males (even if it is mostly sub-concious).
If this theory is the case, then men certainly should not shave. Why? Well, females want to be looked after by their male, something pre-pubescent boys (as indicated by lack of hair) can't do. Hair on males define them as Men, lack of hair define them as boys.
To loop this theory back to its beginning, Men want to feel they have someone to protect and look after, someone to show-off to. Women (indicated by hair presence) are self-sufficient and are unimpressed by show-offs, where as pre-pubescent girls (indicated by lack of hair) adore their Men.

Therefore, women shave their legs to appear younger, but don't expect men to as they want them to appear older (also the reason for men to grow facial hair).

Please note, this write-up is merely a hypothesis of "Why (American) women shave their legs" and operates entirely on the the stated theory.