Well, I firmly disagree with the thesis (though I agree that you can't nab a strangers sunglasses, no matter how much you want them and feel truly deserving of them). The premise that sharing isn't a practical skill is hogwash. I share all day, every day, every minute, constantly. We all do. We share offices and time with the barrista at Starbucks and space in the elevator and books at the library. People job share and carpool. When it comes to friends and family, I share dresses and punch bowls and bicycles and wallpaper steamers. Sharing is fantastic (and environmentally friendly).
But the real point, which is why I think the article kinda sucks (there I said it), is that sharing teaches patience. Sharing is a vehicle for the lesson rather than the lesson itself. By asking your child to use a toy and then share it, you're asking her to be patient, fight the instinct of "ME, NOW" and wait her turn. While you may not agree with my characterization of waiting to order your Starbucks latte as "sharing", you can certainly agree with my assertion that patience is possibly the most important lesson of all. It's not just a virtue, it's life. And whether your little one is patient, or not, she will be required to wait on a daily basis from now until infinite.
So, back to the toy policy at the author's school (which I kind of like by the way), whether the author believes it or not, this policy requires sharing. At some point, all toys are put down, if only because school is over. And you can damn well bet that if Timmy made Tommy wait all afternoon to use the ball on Monday that Tommy is beating Timmy to the ball on Tuesday and making him wait all afternoon. So whether it's in five minute intervals or alternating afternoons, sharing is happening at her child's school and it's a good thing because it teaches patience.