It is true that there is some subjectivity and potential sample size bias, but when you regularly see large numbers of coins that are graded differently then it no longer becomes an issue of subjectivity or mild inconsistency on a few coins here or there. Even the services have admitted that their standards have changed (not specific to any series). Salzberg did an interview that is somewhere in the NGC archives and Home Run Hall admitted to the old, more conservative early years of PCGS.