Why do men keep the racket head in front of them, and women take it behind them?
It dictates the kinetic chain that you'll use for your stroke, again whether the FH will be a pulling stroke or a pushing stroke. I can't emphasize this point enough, because the motion of your backswing is dictated by the kinetic chain you use. The pushing model is what's espoused over at easitennis, and if you look at the frame shots used there, it's very different than what the men do. The pulling model is what's espoused at jco's hi-tech tennis site. If you try using one paradigm to explain the other, it'll completely confuse you. But it begins with the racquet head/tip.
The pushing stroke is actually the more powerful one. You end up using the same muscles that you would with a bench press (i.e. the triceps are an active part.) Also the optimal contact zone is much higher; even with an Eastern grip, you can pound a ball that's at eye level. Also, the way the torso and legs work is differently. In the ATP model, a lot of racquet speed is contributed by torso rotation, because the energy from twisting your body can be directly transfered into the pulling of the arm. However, in the WTA model, it's the legs that contribute this power; the pushing off the backfoot transfers energy into the pushing of the arm through the forward swing. Finally, though their backswing is very circular, the actual forward swing arc is inherently more linear than the men's. It's because as you press forward, your elbow will always go into your body. You don't need to slot your stroke. As soon as it can't go anymore, than the racquet comes around the body.
There's however three big caveats with the pushing stroke, and it's reflected in the WTA power game.
1) First, you get much, much less natural forearm pronation. With this chain, it's difficult for your forearm to supinate a whole lot in the backswing without the racquet opening up too much. So, you're going to get a flatter stroke.
2) Second, the contact zone is also very high. Even with a true Eastern grip, you'll want to hit balls near your sternum, not at the waist. For that reason, most of the women learn very early to stay very low to the ground and inititate from a sitting position. But if you're a Sharapova and 6 foot, you have a very difficult time dealing with somebody else who can hit low, flat shots consistently below your zone. Which is her problem, if somebody keeps dishing out power, her errors go up and her legs eventually fail.
3) Third, the down-to-up motion is inherently limited with this stroke, since you really can't swing at waist level. Therefore, much less topspin. As a result, it's more difficult to play defensive shots on high bounce surfaces, unless you change up your grip. But if you change up your grip, your already high contact zone goes even higher.
There's however advantages to this stroke:
1) A lot of power comes from movement. Meaning, if you're running around, your power automatically goes up, and you don't need to set up with a big unit turn to smoke the ball. Which is what Sharapova and Venus Williams can do.
2) You can keep building more and more power by increasing your lower body strength. Having powerful legs like a Kim Clijsters or Serena Williams, enables you to explode into your shot. Now, it's true that you may have problems reigning your shot into the court.
3) Because torso rotation is not as important with this stroke, timing isn't as important. Once you've figured out the trajectory of the ball, just get your feet to go and aim.
IMO, both men and women are modern. One thing, though, is that the women tend to keep their racquets on edge more often than the men. Only a few like Serena, Venus and of course Henin have a relaxed wrist, which gives them more topspin and power in their shots with less effort.