I have two theories:
1) That they are on every mixed Christmas CD collection i've ever listened to, and every Christmas movie I've ever seen. And I happen to be listening to them or watching the movies when I am doing other Christmasy things so as to heighten the Christmas spirit and make a lasting impact on my Christmas memories and associations.
or 2) That that evil wizard Tchaikovsky somehow recorded subliminal messages into the score and those messages brainwashed me when I heard each of those songs. I can totally see him working in his basement, or perhaps his 3rd floor musical study in a tower (I always dream of writing music high up in a tower. why? I don't know, but i picture this:
being like, I will show them. Anyone who ever listens to this will be eternally unable to properly celebrate Christmas without me! It sounds a bit sinister, and perhaps a little blasphemous, but whatever it is, he's done it.
Anyway, go test my theories. I dare you to tell me you could only choose just one theme.
To pay tribute to this fact, today Sean and Julian and I are heading up to see a condensed, kid-geared version of the ballet because the music tells me that I must. Merry Tchaikovskymas!