I believe this was true back in the old cable driven speedo days, but today's speedo is electronic. On Chrysler designs, the transmission uses a output shaft speed sensor that is basically a switch that opens and closes to create pulses. An integrator converts the pulses to a voltage, and either an ADC, or CPU places the voltage to the speedo. I suppose there is some error, but I would assume it would be linear error in an electronic speedo?
It still uses a needle that sweeps across a 270 degree arc, it's not like it is digital.