I say the goal is to minimize non-convexities, which in this context means avoiding the possibility of no mail or UPS deliveries for two days running. That makes Saturday and Monday especially bad days to have Christmas.
When Christmas is on Wednesday, as it was this year, on that Wednesday you still can be reading the books which arrived on Tuesday and then a new lot comes on Thursday. The public libraries also close for only one day, not two or three in a row.
Christmas on Wednesday also means that the roads are deserted for all the other weekdays, since many people end up leaving town for the entire week. Then you can visit all those ethnic restaurants you wanted to get to in Gaithersburg or Mount Vernon without hassle.
And if you are taking a vacation abroad, and trying to use a limited number of vacation days, you certainly don’t want Christmas to fall on either a Saturday or a Sunday, which in essence wastes a granted day off.
You know what is also good about Christmas on Wednesday? It means New Year’s Day will be on Wednesday too, double your pleasure double your fun.