In Japan Xmas is about everything BUT religion, it's not even about presents, it's a very straightforward celebration crowned with a cake and some KFC (or covenience store chicken legs for those who were not cautious enough to plan ahead but still want to jump in General Sanders' gift to Japan's portfolio of imported habits). It's not even a day off, almost everyone works both on December 24th and 25th and then go have a few drinks with friends and or family.
Now, that does NOT mean Japanese Xmas is not a big deal, it's just as important as Halloween and Valentine's Day! Everything has santas and Xmas-themed decorations, let alone the huge illumination in almost every city and Xmas trees everywhere. And this is exactly why Japanese Xmas goes way beyond any other country's party: it's just about the party itself and the people you spend it with, nothing more. No imaginary creatures flying around dishing out presents or being born sans conception under a sentient star, just about people meeting people and spending, quite a lot of spending.
Now many might jump the gun here and and say "that's blatant consumerism!" and that assumption would be entirely correct except for the fact that there's absolutely nothing wrong with that here. Consumerism is considered by some as a social "vice" or "disease" that pushes consumers to purchase goods in an egotistical never-ending race for status against one another, and in that sense, I have to agree I the criticism. Nevertheless, in a society whose 90% is composed by middle class spenders with very comparable amounts of disposable income, well then most people have acces to pretty much the same options and possibilities. As a result, this consumerism actually makes it all about sharing, which is what many people would agree that is Xmas' ultimate purpose.
Long story short, as in many other social arenas, Japan beat "western" societies to the ultimate purpose via de facto egalitarianism. Another involuntary success or simply the natural outcome of creating a society where processes serve people, not the other way around.