I think most people get that. :) But where it gets a little trickier is where individual wishes are concerned. If I, raised in a theoretically protestant but actually pretty much just sort of "American pop Christianity" household , wish my Jewish friend "Merry Christmas!" am I being inclusive or being a jerk? Society hasn't entirely worked it out yet.
For myself, I feel like we should err on the side of goodwill. Certainly if said Jewish friend wished me a Happy Hanukkah I would not feel anything but gratitude. The fact that I don't observe Hanukkah is actually irrelevant to the discussion! My friend is engaging in a religious observance and is wishing me well. What could possibly be wrong with that?
"But Gneech!" I hear some theoretical strawman objecting. "He's othering you! He's making a point of bringing up the difference between you, implying that he is part of the group and that you are not."
Well that's the thing, I did establish that this is a friend we're talking about here, and when in doubt, I believe in working from the assumption that people mean well. If someone offers me well wishes and my response is to read snobbery into it, that says more about me than it does them.
"But Gneech!" says the strawman again. "It's easy for you to say that! You are in the position of privilege here, Mr. White Pseudo-Christian Dude. When someone is othering you, you barely feel it. For somebody who's already on the receiving end of social stigma, it hurts much worse."
Well... it's a good point, strawman. And I don't have a compelling argument against it, so I won't make one. That's why I try to make a point, when broadcasting generalized holiday wishes, to emphasize that I mean "Merry Christmas" in a very personal way. It's a day that brings me a lot of happiness and warmth, and I want you to have happiness and warmth too, whatever you want to call it. Love Everybody Day is just as good a name! 
Merry Love Everybody Day to all, and to all a good night!
 Honestly? In beliefs and practices I'm closer to Hindu than anything else as far as I can tell. But I still put up a Christmas tree and find a lot to love about the season. My spiritual life is peculiar.
 I don't care about "keeping Christ in Christmas," seeing as how He's a Johnny-Come-Lately to the holiday anyhow. But that's a big and thorny post for another day and I don't know it merits all that much. If it's important to you, by all means be as denominational as you like and enjoy it.