It's such an interesting point that you make, AP, about Serena. She's almost always been distracted by other things in her life, but also (until recently) always great enough to drop in and pick up a big trophy. I think you're right that she loves the competition more than she loves the game, and she loves showing up her detractors. She plays with a bit of a chip on her shoulder, like Novak, if you ask me. Whatever motivates. But now, at 39, and the desire to add to her family, the desire for #25 might not be enough to get her to sacrifice for it...and let's face it, it takes more sacrifice at this age.
I also agree that Venus does, however, play for the love of the game. And to quote one of her more vocal detractors around here who would shove her out of the game...KMA.