SWell that may be, but if you have a state sponsored denomination which I understand many European countries to have, then people in school are only going to get that view of religion and it will be very biased to. With the US system at least the bias is to ones own denomination and not inflicted from above, perhaps of a different denomination or religion, making you feel persecuted.
Dont misuderstand me, there is nothing in our constitution that says a teacher couldnt explain the religious differences that caused some of the wars in European history, so it would have been fine to have taught that Austria is/was catholic. Its just not a big priority in US public schools, since they dont talk about religion for its own sake. Many US Private schools do in fact have actual classes on religion (they are run by different denominations) and a lot of US children go to these private, religious schools.
The North American colonies had a long history of people immigrating from Europe because of religious persecution, especially in the Northern part (not so much in the south like Virginia which was much more traditional Anglican church, etc.). An interesting thing is that when they got here and set up their colonial governments, they were no better at tolerating people who thought differently than they did than the European established churches had been, so often times some groups would leave the first colonies and move farther inland, or to different places to be able to practise their religion freely.
So by the time of the birth of the US as a nation, you had many different denominations in the country. For instance Maryland had a lot of Catholics i think, Pennsylvania had lots of Quakers, the southern states were mostly Anglicans, and New England had much of the old Puritan type denominations, though also some new ones.
The framers of the US constitution thought (wisely I think) that it should not be the governments role to have anything to do with religion, that should be left to the free will of the people, and could be organized by the churches that the people wanted to support. This extended to schools when the government started public schools (which was many years later) and so it is the job of the parents to teach their children about religion and not of the government. That is why in private schools they teach about religion, since the government doesnt run them, and the parents have control of whether they go to that school or not.
It is interesting to point out that here in the US, where we dont teach about religion in our schools but rather at home or in churches, and where there is no government support of religion, I think that we have much more church attendance and 'practicing' members of churches statistically than in many European countries that have a state sponsored religion and may even spend part of the budget on religious instruction and keeping up the churches, etc. So it seems that statistically, our system works pretty well, if you are looking at it from the perspective of churchgoing as a good thing.