The exponential growth argument would work if there were some intelligence to grow but IMO we haven't reached first base in AI. A humble calculator can perform arithmetic much quicker and much more complex than any human. No intelligence there. Deep Blue can beat us at chess. I see no intelligence - brute force computing speed and heuristics. Watson, nope...
Steven Pinker trumps Ray Kurzweil: "There is not the slightest reason to believe in a coming singularity... Sheer processing power is not a pixie dust that magically solves all your problems."