By the way I watched Sharapova's video after replying to your post. And I don't see even the slightest lag there. It only confirms what I already said before. When we talk about 'the lag' we don't mean taking the head of the racquet all the way back and start the forward swing but rather the hand starting the forward swing while at the same time the head of the racquet going backward for a split second, than catching up with the forward moving wrist towards the contact. I'm too busy to find one at the moment but watch Federer's slo mo forehand side by side with Sharapova's.
You'll see the lag if you look for it. The place to observe that there WAS lag is to look at her racket and wrist at and through contact. Her racket goes slightly further back to 90 degrees when she initatiates the swing (for example at 0:01 in the video). Approaching contact the racket clearly catches up... reducing the forearm-to-racket-handle angle significantly, the whip that betrays the lag's existence. The whip of the racket when the hand pulls to the left an instant before contact (for a rightly) is one value of the lag. Another is that the lagged racket's inertia causes the grip to press against the palm, insuring racket stability through the swing to contact, the hand and loose wrist transferring the racket's weight in lag to the large muscles of the forearm....stretching those muscles, the big spring of the forehand.
McLennan's definition of lag suffices in that regard:
"On the forward swing (said again, the forward swing and not the backswing) the hand pulls on the handle, but the racquet head actually delays, lagging behind, then catches up in a whipping motion at impact. Note the lagging racquet head picks up speed at impact, with a short yet somehow loose motion. Not a big backswing, not an enormous follow through, but serious racquet head speed at impact."
http://www.tennisnow.com/News/Featured-News/The-Modern-Forehand-–-the-secret-is-the-Lag.aspx
If you think that lagging the racket MEANS visibly throwing it one way while the grip is being pulled, it's simply a matter of disagreeing on the definition. I don't think it means that. Sharapova, just as an example, lays back the wrist intentionally in her back-swing, achieving the forearm-to-racket angle that a typical ATP player only reaches when he's rotated forward about 45 degrees. That doesn't mean Sharapova's racket isn't lagged, isn't "lagging behind" her hand, pressed against her palm by its inertial. On the contrary, it simply means that she achieves that relationship.
Put another way, first-rate WTA forehands do not give up the benefits of wrist lay-back and racket lag, or of initial upper-body-momentum transfer to the racket via external shoulder rotation at the start of forward motion. What a good WTA-type forehand gives up (vis a vis the so-called ATP form) is compactness of the swing, violence of the lag, and extent of ESR and then of ISR into contact. The elements are all there, simply in less compact and slightly (for most...) less muscular form.
That is my view on the thing. There are others, I'm sure.