Also, I think the point of the paper is that growth gets harder, not easier. From that perspective R&D spending should have increased massively in constant currency to keep pace, not decline even slightly.
Looking at it from the other side of the mirror, there's probably some other suite of factors that causes both things. Taken as a prisoner's dilemma, defecting from R&D may be perceived to have a payoff ( those engineers talk funny and cost a lot ) which saps R&D and also slows growth.
I think that in an increasingly specialized workforce, the management team has less bandwidth to apply to R&D. One stump hit and it's done for. Successfully leading R&D has little payback in the larger economy; leading M&A is better understood. This is a corollary of the general "tower of Babel" problem.
Remember that Amazon is slightly a tribe of madmen to most business types in large companies.
