This line: "Kurzweil calls it the law of accelerating returns: technological progress happens exponentially, not linearly."

He doesn't bracket his law with exponentially to a 'certain point' or 'is currently happening'. He claims it is a law that all technological progress currently happens and will always happen exponentially.

Perhaps I am misreading him, but I interpret predictions as claims that exponential growth will always continue.

Anyway. That aside, You can't use an exponential curve to make predictions about the future if you accept that the curve will end at some point. If you accept the curve will change and you can't know the point of change then you can't use it to make a prediction.