Just a guess: there are probably people here who would like to know what justification there could possibly be for ratios other than "as close as possible", because close is better.
Given: GM had some idea what they were doing, and their purpose in selecting parts for what would be essentially a main-stay auto transmission - why wouldn't they just provide closer ratios?
Because closer is not better, closer is different. "Better" depends on the entire vehicle.
Example: a diesel is designed to have good torque with not much peak power. Why bother? A gas engine can have equal torque, and even higher power.
Because diesel torque occurs at low RPM that you use all the time (which is not possible with a NA ignition engine), that's available in any gear without downshifting, that "feels like" a far bigger motor. For engines with a broad and low speed torque curve, losing RPM on shift is less important than covering the widest range of vehicle speeds in MPH.
