Partly women fear being too aggressive and feisty - which can be viewed as negative in the workplace - but I think it's more complex. It is part of our conditioning that men equate money with status and power but women see job satisfaction as more of an issue.
Women are more likely than men to think, well, I'm good at my job, so I will be noticed and promoted, and I will eventually get a pay rise. Men, on the other hand, will go to their line manager and say they deserve a pay rise... now.
ADDED: Suddenly, I realize I need to just say to you: I think that you should value this blog and show your appreciation in dollars. There is a PayPal button in the sidebar to use whenever you want, and here it is, to be forthright and clear in a manly way:
If you read every day, I recommend $20 a year. $5 or $10 would also be good. Or just toss in $1 whenever a post makes you feel you've really gotten something worthwhile.