steppemum - Muslim Buddhist countries are different in lots of ways - they don't have the same herritage us us. You could just as easily argue that the English language is inherently Christian because it's isn't (much) spoken in the Muslim world.
If it were the case that Jesus was central to Christmas having a meaning, then it would have largely fallen out of significance in the UK, along with church attendance, baptisms and all the other parts of Christianity that really are about being a Christian.
But it hasn't - and that's because it does have real meaning to people who are not Christians. It's our family celebration of life, family, being together, giving presents, sharing food, and closely tied up with new year and thinking about the year gone and the year ahead.
In contrast, say, Easter I think is largely a Christian fesitival. It means nothing to me really, other than being a couple of bank holidays. But don't try to tell non-religious people with a UK heritage that Christmas can't mean anything to them, when they're all of them describing what it does mean to them.
And yes, whilst Jesus is a historical figure, I don't think the historical evidence of him having been the same baby as was born in a manger in Bethlehem (maybe) is so strong. Still less the evidence of the three wise men standing over the crib bearing gifts - which even the bible says happened sometime later, but still forms part of every nativity scene - it's a lovely story about a baby born in poverty who went on to achieve great things - and that is a meaningful story to anyone in the world (unless you're from a different religion that expressly forbids you from taking part in anything Christian)