Why would you think of things to the base million though? >_> Base thousand makes more sense because we (the Western world) think and write numbers in thousands (,000), so billion is basically the next thousandth after million.
so basically
1 - one
10 - ten
100 - hundren
1,000 - thousand
10,000 - ten thousand
100,000 - hundred thousand
1,000,000 - million
10,000,000 - ten million
100,000,000 - hundred million
1,000,000,000 - billion
etc.
In science, base 10 is the most important base number, followed by the base 1000 (kilo, mega, giga, milli, micro, nano etc.), so it makes more sense to follow the base 1000 numbering.