If I thought that the circuit and ADC combined are going to be up to the difference between 1/1024 and 1/1023 then I might take more care in making the shortcut abstraction.
Jack joggled me in a PM with a section of the datasheet that made me think hey, one solution would be to never feed the ADC the full AREF range. If AREF is 5V then what extra circuit would be best to limit that to 4.8V without more trouble and current drain than the difference is worth?
FWIW Robin, I'm sorry I stepped into it too.