Some people insist on using "happy holidays" as a replacement for "Merry Christmas" as they feel the latter isn't all encompassing of how everyone views that specific holiday. Personally, I use Merry Christmas and a Happy New Year, but do not get offended when someone says "Happy Holidays".
But, a greeting, is a greeting, is a greeting. I have never understood why there has been so much focus on which greeting to use in recent histort (well, I do understand, I guess...).