Dollar price is without tax because there is no sales tax for online purchases in the US, at least in most states (Or is it that you have to pay sales tax only if you live in the same state as the company you buy through? So if you buy through Steam you only have to pay sales tax if you happen to live in Washington? Or is that a myth? Its not easy).
Euro price is with sales tax, for example 19% in Germany. That means its effectively cheaper here. Some countries actually "introduce" sales tax for games/digital products this year (Switzerland, South Korea, New Zealand, India, some others) because they didn't collect it until now which might raise prices in these countries.
I would happily engage in a discussion about tax systems and tax "optimization", but I fear that is beyond the scope of this thread.