It may be simple math ... but it is also an irrelevant technicality by which people attempt to make themselves feel superior to everyone that is celebrating a new decade.
For the record, 2010 kicks off a new decade if you started counting with 2000. It doesn’t matter where you started at the beginning of the calendar ... it matters where you started for this 10-year period.
SnakeDoc
Yeah, let’s get on to more important things — like is it “two thousand and ten” or “twenty-ten”? Or, will there REALLY be a “blue moon” tonight....
Anyway, Happy New Year to everyone!