that is true to some extent, i.e. the analogue to digital conversion can only divide the 5 volt signal into a certain number of 'chunks', so each chunk of the 5v will be a greater pressure when using a 5 bar MAP sensor

but it doesn't mean that you have to use the whole 5 bar scale in your maps, so the interpolation going on there needn't necessarily be much different

nothing wrong with interpolation of the map anyway - it's certainly better than running off the map imo