I am from the E.U :) . I also work for public administrations and have close relative working for E.U administrations, so I do have some knowledge about how the beast operate.
> The EU rarely bets on a single firm in a single country
Indeed, except when they do. While the various E.U administrations like to usually create funds that are distributed with grants (which are rarely evenly distributed evenly amongst the member mind you), there is sometime where they do invest in one horse. This is usually in high-tech, high-capital sector tho', like Airbus, Arianespace, where there is only a very few competitor, and the chance of having new one is very low has the investment in time and money to get a business up and running would be basically only feasible by a state.
So I don't think Mistral is that (yet at least). But it is still the only company operating at this level in the E.U (for now), making it a decent bet for ASML. Plus, as many pointed out, there is also the French connection :D