I think that things are "perfect enough" to whatever tolerances you desire or can measure.
When the need for improved accuracy becomes apparent then a new level of rigour in measurement is devised.
Witness the changes in the standard metre, defined originally as the distance between two marks on a metal bar in Paris, then later as the number of wavelenghts as stated above anf I beleive that they are considering a new standard now as the old one is not good enough.