I'm with Tennisfreak and isilra. The poster tricky has written a lot about the differences between the ATP and WTA forehand techniques. As Tennisfreak points out, the ATP technique uses the stretch-shortening cycle at the forearm and shoulder to generate greater RHS. RHS can be used to produce ball speed, ball spin, or both. The women generally have enough RHS to generate good ball speed and moderate spin. The men can hit the same speed with an extra 1000 rpms of topspin, or flatten it out and hit 100 mph winners. There is also something about the rapid pronation of the forearm that seems to generate "free" spin, especially for guys like Nadal and Federer, who, like isilra points out, use funky pronation-supination-pronation technique. The women tend to wipe by creating an arch with their elbows (internal shoulder rotation) while the men wipe from the forearm and wrist.
Why don't more women hit like the men? Maybe it has something to do with grip strength as kids. To hit the ATP stroke there is a whip or lag in the transition between the takeback and forward stroke. This takes quite a bit of grip strength, especially in the thumb. It may be that little girls aren't strong enough to "whip" the adult size racquets they are given as children and must layback the wrist before the forward swing starts and use lots of trunk rotation to get that big racquet to come around with speed. Boys are stronger, especially in the wrist and shoulder, and so might find it easier to whip their racquets like they see the ATP players on TV do. They also are strong enough in the shoulder that they don't have to rotate the trunk so much and instead are able to harness the power of hip snap.
There also might be a coordination issue. The ATP forehand is a bit like a sidearm throw. The old phrase "throw like a girl" is often referenced when talking about teaching young girls or women to serve; this issue might be involved on the forehand too.
But how to explain the case of Raonic? He's a big guy, and obviously has good throwing mechanics with that monster serve. But he's got a WTA-style forehand and can't generate enough spin to harness his considerable power. In his case, I'm not sure he will make it to the top 5 without retooling his forehand as Henin did. According to John Yandell, she and her coach hit the video archives, focusing on Agassi in particular, and managed to create an ATP-style stroke for herself. Don't see why Raonic couldn't do the same.