This is not about science increasing the rate of scientific progress. It's about computation improving the rate of computational progress. Particularly, the "Singularity" is about that happening in a world where strong AI exists.
And I'm not even going to harp on the fact that the number of computations per second that we perform on this planet has been undoubtedly exponential at least for a while, because that's not the real point.
The real point is that like the author says, human creativity is still the driving force in computational advances, and human creativity can't be sped up by periodically doubling clock rates or core counts.
If it could? Those doublings would happen even quicker, and the exponential growth we've seen so far would be nothing.
This does, of course, require that you believe that strong AI is possible at all, and that the entire process of creativity could eventually be put into software. If you don't believe in that in the first place, then there's no point having the argument at all - you don't argue the details of a nuclear chain reaction with someone that doesn't believe in neutrons.