Jano_OddKidd, This depends on the ecu/chip, some use MAP and TPS to
estimate load at idle which stabilises fuel delivery in a pulsing manifold and to
some extend it ignores the map sensor input for a portion of time.

It is a fact of electronics and mechanics for that matter,
all components are built to a tolerance and when a part is made of many
such components, the tollerances add up differently.

Map sensors are accurate enough for the job they do but their range
will drift with age/temperature and use.
These are not laser trimmed during production otherwise they would cost
10 times as much.
Remember, It is a mass produced part after all and built to a cost.