I said nominal, not average.If you mean that it was done with the intention that all European countries would, as a consequence, gradually move to actually providing a supply of average voltage 230V, then that would make sense.
AIUI the intention was for an eventual harmonised supply of 230V nominal, ±10%
It would make a great deal of difference if you needed to use the nominal weight of a loaf in calculations.If a 'standard loaf' were required to have a weight between 0.7 kg and 1.3 kg, it would make no difference to anyone whether it were described as having a 'nominal weight' of 0.7, 0.8, 1.0, 1.2 or 1.3 kg, provided enough additional information were provided to allow one to determine the minimum and maximum permitted weights.