I'm confused (shut-up ladies!) you want them to be included in what exactly? If someone isn't a christain why would they want to be included in Christmas?[/QUOTE]
I think she meant she wanted everyone to have a happy holiday season, no matter what they celebrate. Just because someone isn't Christian, doesn't mean that they don't celebrate something. There ARE other winter holidays that coincide with Christmastime, such as Hannakuh and Yule/Winter Solstice. That is the main reason for the term "Happy Holidays", because there is more than one during this time of the year. Hannakuh has just passed, and Yule/Winter Solstice is this weekend.
About the topic of Jesus not being born in December, most scholars and religious experts DO believe that this is true.
The main reason that it is celebrated in December, is because being Pagan used to be as common as being a Christian was. The colors red and green, and traditions such as decorating a tree and decorating with pine greenery are actually Pagan traditions during the time of Yule/Winter Solstice. This has happened with many other holidays as well-which is why a decorated tree or wreath has nothing to do with the birth of Christ, and pastel colors, bunnies, and coloring eggs has nothing to do with his resurrection.

All of these traditions are actually Pagan traditions. (Which is the main reason why some stricter Christian religions don't do these things...)
When certain people started promoting Christianity, and wanting people to stop doing Pagan practices, they started celebrating things like Easter and Christmas at the same time as Pagan holidays (to slowly replace them) instead of when they would have actually have happened. This is why Christmas is celebrated in December, and not in the autumn or late summer, when it was more likely that Christ was actually born. The spring celebration, Easter, actually still has a derivitive of the Pagan holiday name-Ostara.
However, even though they changed the dates to replace other holidays, some of the older traditions of these holidays-trees, wreaths, cranberries, red and green-all the way to bunnies and colored eggs-stuck.