Tying currency to locale seems insane. I have bank accounts in multiple currencies and use both several times per week. Why does all software on my system need to have a default currency? Most software does not care about money, those that do usually give you a quote in a currency fixed by someone else.
It's about how easy it is to reach the € sign. Ideally, it should be as easy to type as the $ sign is in the en_US layout.
For what it's worth, I think most all European keyboard layouts have key combos for € and $ defined (many have £ as well), while on en_US you can only type $ (without messing with settings). Europe of course has more currencies than just €, but they use a two-letters-long abbreviations instead of a special symbol.
