It cerainly depends on the budget you are wanting to spend. Real beds (well, an approximation of a bed that you would still sue a hotel over, but still a million times better than reclining seats) are expensive in Europe as well.
But if you compare it with the price of a flight with a level of comfort well above the cheapest class, which is fair even if you wouldn't spend so many hours in the "cattle-flight", the difference is no worse than in any other plane/train comparison (yes, rail travel is expensive, but it will become more competetive with every increase in energy price, which, in the long term, is inevitable due to scarcity of resources).
Maybe the biggest difference between Europe and the USA is that the regional rail systems offer pretty good service, certainly better than airline service to the various mildly backwater places. If you travel by plane you will often switch to a regional train for the last 100 or so kilometers and many airports are very poorly connected to the railway system. The place where you get off the night train, by definition, is connected perfectly.