It looks like the reasons why this DLC has the same price in euro and dollars is not understoodby many people so I will try to explain it.
I happens for mainly 3 reasons:
-the difference between VAT (value added tax) between Europe and the U.S.A. This tax, applied to videogames too, makes everything more expensive in Europe, basically. There is some kind of VAT also in the U.S.A., but it's much lower;
-on average europeans are willing to spend more than north-americans for videogames, so when a new game costs 50-60€ in europe, pricing it 80$ (when that follows the right conversion rate between the currencies) in the U.S.A. would make it too expensive for many people;
-the companies that sell videogames need to mantain the "psychological effect" of prices such as 9.95€/$ or 29.99 €/$ or 49.99 €/$ or whatever, so the easiest solution is to just leave the price unchanged, even if a € is currently worth more than a $.
I will end saying that this happens for most of the games, on steam and elsewhere, not just for this DLC, and yes it can be annoying.
By the way I think it's an excellent price for such a DLC, since I enjoy M&M very much, and I know the devs put a lot of effort into NW.