The thing about 12 is that it is divisible (*crosses fingers*) by a lot of numbers which makes it very suitable for creating patters. Don't know if that's the reason yee oldies used it though, but it would make sense.
The thing to watch out for in these matters is conformation bias (I want credit this time!!!) though, when you're researching the claim whether 7 occurs so many times, you'll start seeing the number 7 appear everywhere. So the only painstaking way to say anything about this with certainty is to documents all occurrences of all numbers in as many mythical stories possible before you really can say anything about which numbers are most prevalent.
But the possibility that there may be numerical thought patters inherent in how we perceive things is interesting none-the-less.
