Hi Scott,
Many people, especially the irish catholics, are not convinced by the argument that this word's history makes it acceptable in their language. They claim that people aren't writing it for that reason and I would agree.
Writing out 'Christmas' thousands of times by hand on scarce, expensive parchment would have indeed been a waste, especially during a time when the abbreviation was understood.
But our era is a different one.
I guess it really doesn't matter, only that it's part of the whole degeneration of what is personally important for many people.