Only if you take 'ten times smarter' to mean multiplying IQ score by ten. But since the mapping of the bell curve to numbers is arbitrary in the first place, that's not a meaningful operation; it's essentially a type error. The obvious interpretation of 'ten times smarter' within the domain of humans is by percentile, e.g. if the author is at the 99% mark, then it would refer to the 99.9% mark.
And given that, his statement is true; it is a curious fact that IQ has diminishing returns, that is, being somewhat above average confers significant advantage in many domains, but being far above average seems to confer little or no additional advantage. (My guess at the explanation: first, beyond a certain point you have to start making trade-offs from areas of brain function that IQ doesn't measure; second, Amdahl's law.)
Yup, that's the way I interpreted it too - going from top 1% to top 0.1%.
Recently I stumbled upon Richard Carrier's essay "Are We Doomed" (June 5, 2009), when asked to comment about the Singularity, said the following:
What do you think?