When it comes to clubbing in Vegas (and elsewhere), women definitely have the edge. The nightclubs want hot young female bodies populating their venues; the rule of thumb is: Wherever there are women, men follow. Subsequently, the men buy the expensive drinks and bottle service to impress and hook up with the women.
So the clubs "encourage" the women giving them whatever preferential treatment they can, such as being hustled to the front of the line, reduced or no cover charge, ladies nights, etc.
In addition, the higher cover charge for men affords at least a little protection for the women by keeping the gender ratio at least equal, or tilted toward the distaff side. (This is especially true at the topless pools, where the men want to show up and gawk at bare breasts and those attentions aren't conducive to relaxing sunbathing for the possessors of the same.)
All that said, if a club is really busy, such as celebrity night at Hakkasan or XS, just being a girl, even hot and underdressed, is no guarantee for preferential treatment or even getting in at all. On busy nights, there'll be 100 other hot girls begging the bouncers to get through the door of a club where a few thousand people are already packed in.
That's why we recommend a little strategic planning, for both men and women. Contact a club host to secure a spot on the guest list. Arrive at the designated time (pre-arranged with the host), check in at the designated place, and be ready to grease a few palms along the way.