I think his proposition is roughly, that a singular technology grows on an S-curve, but as each one technology slows another picks up the baton and runs with it, and the totality (sum of S-curves) has historically looked exponential, and promises to continue.
Ahh, now that is an interesting angle, but that would suggest that the rate of introduction of new technologies is linear and that every new technology must have a period of exponential growth initially.
(Or I suppose... That the rate of introduction of technologies with initially exponential growth rates is linear. You could ignore those without exponential growth rate provide that a constant number did.)
I think basically at any one time there are a lot of competing new-born technologies, and it's only in retrospect that we can see which of them will go exponential through a feedback cycle of improvement and growing adoption.
It's not so much that technology always goes exponential. It's that in retrospect, we notice the ones that did.
