Honestly, I'm astounded. I agree that 1950-2000 has nothing comparable to telecommunications, while 1850-1900 and 1900-1950 did, but I think its obvious that telecommunications/computation effects from 1950-2000 swamp 1900-1950 which crushingly swamps 1850-1900. A tiny number of telegraph lines surely had very great impact given what they were, but WTF?!?
Also, it seems to me that the telecommunications of 1900-1950 remain the single biggest element of tech change during that time for all the impact of everything else.

A major question regarding the rate of change is "for whom". Things have changed less for elites than for the masses, as much tech consists of inferior goods, substitutes for things that elites accomplished via human labor or via the ability to pay high rents. For a Chinese commoner, things have changed more in the last 40 years than since the first cities. For ordinary non-intellectual Americans, the last 40 years have seen little significant change and what change has happened may actually be dominated by the improvement in food quality!