A perfect example is the Christmas scene in Harry Potter and the Sorceror's Stone (Philosopher's Stone in the British edition). This scene, with Harry waking to more presents than he's ever seen in his life, is reflective of the character of the Dursleys and the past that Harry is dealing with. It communicates something about the character without feeling thrown in there at a whim.
Many other fantasy stories don't include holiday/feast day scenes at all. In considering that, I lean toward the thought that the main reason is the possibility of that holiday/feast day scene not moving the story forward at all. But perhaps another reason is that authors tend to not include holidays in fantasy because religion is one of those topics than can be almost totally ignored in any story that doesn't deal directly with it. I think that's why the religious fiction genre exists really. To give writers and readers the opportunity to create and enjoy stories focused on religion as a primary topic.
Consider this as an example of religion being pretty much ignored in fantasy fiction: The gods of the Lord of the Rings trilogy are modeled on Norse tradition -- chief god Ilúvatar is called the "All-Father" as Odin was -- but the only reason we know this is because of materials published later. I'm specifically talking about The Silmarillion and other works. Nowhere in the main text of The Hobbit or The Lord of the Rings do we hear even a mention of the gods of Middle-Earth. No invoking of the gods even to swear that I can recall, which is something fantasy authors are wont to do (myself included).
Religion has been a part of human existence since the first thinking people evolved. It explains the world around us, and gives the believers something to look forward to after death or strive for in this life. Why then do authors tend to ignore that facet of society in fiction? Is it because religion only sells in religious fiction? Or is it because the focus of the story doesn't require religion as a touchpoint?
What do you think dear readers?P.S. The Ten-Word Novel Contest will close on Thursday, December 31, 2009 at 11:59 p.m. U.S. Eastern Time. Get your entries in!