There are indeed fingerprints and fingerprints. I have a pattern 100 francs in silver from Monaco (1950), graded MS65 by NGC. It has a minor fingerprint on the reverse which doesn't really affect eye appeal; giving it a top grade in a slab seems fair. The bun penny I'm talking about had a subdued finger print on Victoria's face which was clear enough that you could probably use it in a criminal investigation; you had to hold it to the light in order to see the portrait properly at all. I think a coin like that would be better off toned brown than "fully lustrous" with such ugly contact marks. But the grading company didn't care.
Regarding the MS65 criteria...all that PCGS says is "Above average strike with minor marks or hairlines, mostly out of focal areas". I think a fingerprint is treated as a minor handling mark...irrespective of the actual effect on the eye appeal of the coin.