There was no Gregorian year 1, 2, 3, 4, 5, 6, ..., or 1581, either. There is no contradiction in the calendar starting on a 1 but decades starting on a 0; either way the calendar actually started in the middle of a decade/century/millenium. True pedants should be insisting the decade starts on a 2, and centuries start on 82s!
(And for the record, I posted that out of humor, not pedantry.)