Happy New Year, New Decade everyone! I have a good feeling about this one! 

Tying the end of the decade to 2009 is a simple enough misunderstanding, brought about by a belief in some quarters that the current western epoch, variously designated as "Anno Domini" (AD) or "Common Era" (CE) started in 0 AD. Not so.
The year 1 BC was followed immediately afterward by 1 AD: there never was a year zero – at least not in our calendar. It is therefore a matter of easy calculation to determine that the real end of the decade follows in 365 days time – and is not tonight.
Wrong, there are in fact two ways to define the beginning of a new decade. Modern culture is (legitimately) unconcerned with the beginning of AD, since it was actually made up after the fact and therefore there was never actually (In reality) any Year 1, never mind two in succession. Modern culture (Correctly) Ascribes more importance to the change in the numbers. Going from 2009 to 2010 is a more significant shift than 2010 to 2011 and we have been grouping decades in this manner for 50+ Years. To wit, the People's Encyclopedia dictates 2010 as the start of this decade
http://en.wikipedia.org/wiki/2010s .
Additionally, we group numbers generally into X0-X9 sets of ten. In fact that's how decimal Base10 works. Therefore defining the decade as 00-09 makes a lot more sense - especially since nobody is saying "22nd Decade". You're applying the argument against 2000 being the start of the second millennium (The number of years since AD began) to the defining of decades, and in so doing are missing what was actually wrong with calling 2000 the start of the second millennium - the counting part,
not the millennium part.
Truth is dictated by common usage, not by outdated and irrelevant historical numbers. You're being a pedant, but you've failed to note that any period for 10 Years is a decade, making any argument about when a given decade starts completely pointless.

The Frome Flyer: Smoother, Smarter, Calmer,
Winner.
Jenson Button: Professor, Chauffeur, World Champion Racing Driver.