Why do people say Happy Christmas?

[H0merSimpson]

Where has this come from? Have a Happy Christmas. Don't we sing this:
We wish you a Merry Christmas, We wish you a Merry Christmas, we wish you a Merry Christmas and a Happy New Year. So what is it gonna be? We wish you a Happy Christmas and a Happy New Year? Good tidings we bring to Yew and Yorking. Where are these places anyway? Christmas can be confusing you know.

[Gef]

Happy Christmas to you.

[H0merSimpson]

Doh! :o)

[BBWCHATT]

http://www.carols.org.uk/we_wish_you_a_merry_c hristmas.htm