The concept of 0 is the basis of all higher mathematics.
I challenge you to count digitally without using 0
As I stated in an earlier post, 0 exists to count from 9 to 10, 19 to 20, etc.... so yes, it is integral if we are to count beyond 9.
However, 2000 is the zero year when counting down the decade...we count from 2001 (when a full year has elapsed) to 2010 to complete a full 10 year period... which IS a decade.
So, using your fingers (so as not to get lost/confused along the way) count 31 December 2001, 31 December 2002, 31 December 2003 and so on until you get to 31 December 2009... um, that's the one that's just gone by. Anyway, it's at that point you will notice that you have a tenth digit sticking up and unaccounted for... that digit, and you don't need to hold it up 'til midnight on December 31 2010, by all means use it in the meantime, is to count the tenth and final year of the decade.
Yeah, I know, sarcasm is the lowest form of wit...but I was being facetious.