Merry Christmas

Here's the story of what happened to us.  We walked into Tractor Supply, where there is a Salvation Army guy ringing the bell and with a kettle.  We nodded and said, "Merry Christmas" and he answered, "Happy Holidays."  I got torqued off because well, the Salvation Army is a FREAKING CHRISTIAN CHURCH!  It's not like he didn't know to say Merry Christmas to us, we said it first!  Then to make matters worse, we came out and put our change in and he said, "Happy Holidays" and I responded with "Merry Christmas."  Then so did FarmerGeek.  Finally, very begrudgingly, he said, "Merry Christmas."

Here's the thing, if I know you are Jewish, I will wish you well on the Jewish holidays.  If you are Wiccan, I try to wish you well on those days as well.  I respect the same.  When you are saying "Happy holidays" you are wishing me a Merry Christmas, Kwanza, Channukah, Yule, and New Years (Did I miss anything?).  I don't celebrate all of those.  You can't say Merry Christmas to someone because they might celebrate one of the other holidays instead? 

Why is it less offensive to say Happy Holidays to me?