Why there are ten digits and not 12 or 4 or 6 or 7..!!

Have you ever wondered that why there are in total ten digits i.e, 0-9???
We could have any number of digits for counting number like we have the binary system in which only 0 and 1 is there. We can have 12 digits of 7 digits of 4 digits it does not matter, as long as we have zero we can easily do any complicated calculation with any number of digits. Then why ten digits? what's so special about it? why all around the world people came out with ten different symbols to count????
The answer to this question lies in our hands. Those ten fingers from which you will be typing comments on this post are the reason for ten digits. For the early man, his fingers were the most accessible calculator for doing calculations. Hence his ten fingers became the ten digits to calculate...!!!

Well, that's alright but why time is then divided into 12 or 24 hours and not in multiples of ten??