I don't think they factor anything. They just set a day for the comics to come out. Doesn't matter if there is a holiday that week. If the comics get pushed another day because of a holiday, then they just do.
And like I said, I don't think Marvel is stupid enough to be totally ignorant of days that their shipping agents don't work on.
And if for some reason the shipment is a day off because of MLK, like I said, I know where (at least in CT) to go to track it down, so I'll be getting my comics whether they get on the Big Brown Truck or not.