Strangely I always come back to Lord of the Rings Online every Christmas. I'm not even a high level on it and I've never really been a fan of MMO's, yet every Christmas I'll re-install it to wander about. By time December has finished I've usually uninstalled it and forgotten about it again. I think it just reminds me of growing up, reading the books and being at home.
Even more strangely... I do the same, (not at Christmas though). I love your explanation. Never thought or analyzed why I do it, but I reckon it is the same for me. Nostalgia is a strong thing.