Wu is one of the good guys in the math education war. I do not think he was talking about the gifted kids at all. There has been a general association between acceleration and rigor, which is not necessarily true. Also school math is very algebra and calculus centric. I believe some mathematicians believe that the end goal being finishing calculus in high school is not necessarily all that. There're other subjects such as discrete math are very useful and lend it self to differentiation that are not covered in school math.

Anyway, Wu is talking about accelerating half of the class as we have seen in some school district and differentiating the truly gifted kids.