What you are talking about Scorpion is a process called syncretism and it is indeed a very risky business to take the Christian gospel and just place it over another belief system and "christianise it".
this happens anytime people are forcibly made to change religion, or when they see something attractive in another religion and superimpose it on their old beliefs without changing their way of believing.
Syncretism mixes Christian beliefs with other belief systems, so that the result is something that looks like Christianity on the surface, but is still the old belief system underneath.
Syncretism exists when people practise Christian rituals because they consider them magic, or use the Bible to cast spells on people. In India, in South America and in the western world, there are many examples of the way that Christian beliefs intermingle freely with non christian beliefs.
It is this syncretism which leads our Muslim friends to look at our so called "christian" society and wonder about it and therefore our so called christian faith. (for example, tolerance of practises that are condemned in the Bible)
There are two ways syncretism occurs, by importing christian beliefs and practises and attaching them to existing world views and beliefs (which is what happened when Christmas was attached to the yule festival). The result is a kind of Christo-paganism and santa and other practices of Christmas that detract from the Christian message are a good example of this.
The other way is to so dominate another's culture and view as to import not only christian belief, but also the way of worship, so that the look of the religion is that of a "white faith in a black environment." The people I live amongst struggle with this concept, as this is how the Gospel was presented to them, and now the big issue is how to produce an indigenous church. (but that is another story if anyone is interested)
So.. where does this leave us? Christmas was an attempt to celebrate a beautiful event.. the birth of a baby who was born in the purposes of God and was born to die. Christian faith was superimposed over pagan rituals and they were "christenised".
When the world then adopts santa claus in stead of the baby, and when christmas trees and stars take the centre place in celebrations, whose fault is it really?
Christians are putting the Christ back into Christmas, and the millions of people who go to church at Christmas, yet wouldn't go at any other time of the year, show that there is inside this western world of ours.. a deep desire to look beyond the mistletoe, the presents, and the food and find a spiritual reason for the season.
Jovaro, I love your Dutch way of doing Sinterklaas in the beginning of the month of Dec and then keeping Christmas for it's primary purpose to celebrate Christ's birth. Even though it has now become more family orientated, the separation of "sinterklaas" (Santa claus) and Christmas was a step in the direction of using existing practises to share the Christian message and keeping them entirely separate from the gift giving, fun filled. legendary sinterklaas celebration.
Personally in our family, Father Christmas, Santa Claus was a game people played. My sons grew up having an annual birthday party for the baby Jesus to celebrate his birthday. We have a Christmas tree, and we share and give gifts, but Jesus is the reason for the season.