Look at the style that is played to win tournaments, not at who's playing it. Bear in mind I can only comment on what I've seen. I'm sure the early round mis-matches are still just that.
Here are the results of the GS, T1 and T2 tournaments so far this year.
Sydney.. - JH2 d Amelie
OZ...... - JH2 d Kim
TPP..... - Lindsay d Maggie
Paris... - Kim d MaryP
Antwerp. - Kim d SFE
Dubai... - JH2 d Kuznetsova
Doha.... - Myskina d Kuznetsova
IW...... - JH2 d Lindsay
Miami... - Serena d Elena D
AI...... - Lindsay d Amelie
FCC..... - Venus d Conchi
Two years ago, I'd have said all those players except Kim, stay on the baseline, hit the ball with as much pace as they can 90% of the time, and hope they win. Now though ...
* Lindsay is THE prototypical power baseliner. With Monica gone, she's the avatar.
* Serena is another prototypical power baseliner, though she learned to use some topspin off the forehand wing, and a vicious, but complete unhidden slice backhand.
* Justine uses a lot more finesse shots than she did two years ago. (She HAD them two years ago. She just didn't use them as well.) She's gotten really good at getting opponents running when way and drop shotting them the other.
* Kim is a baseliner defender, and more purely so than Jenn or Venus in previous years. She hits a lot of shots with no offensive intent. She's just making you hit another one. And another one. And another one.
* And Venus, at least on clay where the ball slows down, is actually going to net! (We'll see how long that lasts on faster surfaces where she has less time.)
Several distinct styles of play.
And if you saw those finals, there were very few that were just two players running along the baseline whacking a flat or slightly topspinning ball back and forth. Mind you I like those too. When the players are painting the lines. Every fourth final or so. But a steady diet of it becomes old.
The last couple years, the finals were too predictable. One of the Williams sisters playing someone who played like a pale imitation.
When they played each other, there were always a couple of incredibly spectacular points. But for every one of those, there were ten baseline rallies. But now, a lot of the younger players (< 25) who have the ability to generate a lot of pace are all trying to expand and diversify their games. (Not all. Dementieva and Petrova might as well be Dokic and Hantuchova from two years ago.) And for the sub 20 year old, look at what they have to look forward to.
* Jen and Kim will try to return everything.
* Lindsay and Serena can bludgeon them to death without ever leaving the baseline.
* Amelie and Justine can feed them all manner of spins, height and pace.
* And Venus is attacking the net.
Worse, virtually all of them can do something OTHER than what they do best effectively. These are NOT one dimensional players. You can have the perfect game to beat one style, and there are still four or five other elite players with different styles. Players who only play one way are doomed to failure.
NOW what style do you train and train to play?
Do we still have a boatload of 'near-elite' power baseliners? Sure. But unless you're Serena or Lindsay, who only happen to be the two best servers on tour, AND two of the three biggest hitters off the ground (depends where you put Venus), it just doesn't work.
If Venus can't win from back there, Nadia Petrova isn't winning from back there either. Or Dokic, Hantuchova, Sharapova or any of the others. Tennis has become like the stock market. You have to diversify.