In his fascinating novel Little, Big, John Crowley proposes the idea that time does not actually elapse between Christmases -- that at Christmas we simply flip into another time frame in which it is always Christmas and always will be. Then we flip out of it again.
This is certainly how Christmas feels, and it ties in with some ideas Octavio Paz proposes in The Labyrinth Of Solitude, his great meditation on Mexican history and the Mexican character.
In the book, Paz discusses the importance of the fiesta in Mexican life, as a time when Mexicans cast off their masks, the barriers they erect against any penetration of their characteristic solitude, and feel free to commune with others, sometimes socially, sometimes erotically, sometimes violently.
Paz suggests that fiestas, and all ritual celebrations, don't commemorate an event but recreate it -- recreate a transcendent moment when time is dissolved and masks are discarded. This of course ties in with the theological proposition that Jesus is actually present in the wine and the host at Christian communion services -- and more broadly with Kierkegaard's notion that Christian believers are literally contemporaries of Christ.
And of course it explains why time does not pass between Christmases.