Here's An Answer

Apparently the top-grossing Christmas Day film of all time is "Meet the Fockers" (which I in fact also went to see on Christmas Day; review unavailable). In typical journalistic fashion, Msnbc offers a few possible explanation for why this is.

• "'Meet the Fockers' succeeded in part because of an aggressive ad campaign..."
• "[it coincided with] the release of the DVD of the original 'Meet the Parents...'"
• "[it features] the return of Streisand to the big screen after an eight-year absence..."
• "It captured the clash between families, which resonates at the holidays..."

However, I believe there is a simpler explanation. "Meet the Fockers" was about the clash of families from two different religious backgrounds, and Ben Stiller's whole family was jewish. Seeing that Jews compose the major component of the market for going to the movies on Christmas Day, I think that this fact is the most obvious explanation for why the movie grossed so highly. And it is clear that releasing "Meet the Fockers" on Christmas day was quite a smart move on the part of the movie's producers.