The delay is in the electronics themselves such as an msd box or the orange Mopar box
Different brands have different delay. Example, pertronix has about a 2 degree delay @ 5,000 rpm
Msd has a 4 degree delay @ 5,000 rpm so you can curve the distributor to counter act the delay.
Orange Mopar box, about 7 degrees
GM HEI about 2 degrees with a factory module, 7 degrees with these aftermarket ones

Engines produce more torque and hp through the rpm range with a correct curve in them anyways due to piston speed vs combustion chamber design, so we curve the distributor to accommodate the delay also.