I've come to learn that the number 13 signifies a spiral. Twelve (12) signifies the "vicious" circle that begins where it ends, repeating upon itself (like the "clock").
But thirteen is the next step up, that creates the spiral. I read this years ago in Wise Woman traditions... it was in these wise women (witch hunt days) tradition where 13 was regarded as the spiraling ascension of seemingly magic, and hence the number 13 was cursed, like these wise women witches, as an unlucky number.
It seems that 2012, with all the data, myths, science, and speculation signifies something very important... the end of a vicious circle, hence 12. And 2013 will dawn the ascension of that the spiral to its next step.
Check out these amazing videos of our solar system and galactic spiraling. It sure puts a new spin on our perception of things.