The difference in the games I posted and the snowman game is that the Author games are designed to educate and the snowman game is designed just to be silly. If you play the snowman game you will see just how silly it is.
It is possible that since it is a silly game, the designers deliberately kept all religious holidays out of it so as not to offend someone.
I am not defending PBS nor do I believe that they are any friend to Christians, but I do think that Christmas being omitted from this snowman game has nothing to do with any type of agenda.
I just pictured my two year old actually knowing one of the holidays and being happy when she chose Christmas. For an American company to list winter holidays and leave out Christmas is ridiculous and intentional on someone’s part, imo.