The whole thing is hard to sum up all at once, because you're asking a question with multiple layers in its answer. But this is a good summary of it:
Though as a non-Christian, I do get what you mean, [MENTION=15728]AzulEyes[/MENTION]. I might think "Why would atheists celebrate a holiday historically central to Christianity?" But then, as people here have said, that is closely followed by thinking, "Why would Christians celebrate this holiday, anyway?" In both cases, I guess, it's what the holiday means now--not what it was intended to mean--that supports people's actions. My opinion is that some people are okay with that way of thinking, and some people are not okay with the incongruency. Stuff like that, personally, would bother me, so I get where your question comes from.
And more generally, I get what you mean that you want your holidays to be about more than a convenient party date on the calendar. Some people don't see a need for that distinction, but I feel you there.

No offense to others, I hope, just the way my personal values work.