Is this just an american thing?
Here we alternately say "Felices Fiestas" (the equivalent of Happy Holidays) and "Feliz Navidad" (Merry Christmas) and no one seems to make a fuss about it.
I think Argentina is more homogenous in terms of religion. Isn't almost everyone Roman Catholic in practice or culture? America has more religious diversity, and many of those faiths celebrate different holidays around the same time.
But still, the majority of Americans are Christian and celebrate Christmas. And even those who don't probably wouldn't care if you said "Merry Christmas" to them. It's really not a big deal. People like Bill O'Reilly find a few isolated incidents where people complain about overt Christian overtones in a public setting and turn it into a "war on Christmas. " It's just a way to get ratings.
