It's important to note that successful Iranians generally become successful _despite_ the country they grow up in, not because of it. In my opinion, and having first-hand experience with that environment, the credit for this incredible achievement belongs to her and herself only.
I don't know of the details of the Math World, but probably this isn't true. Till now, a country as big as Brazil, one of the biggest economies of the world, never had won none of the most important scientific prizes. Argentina, our neighbor, has 3: http://en.wikipedia.org/wiki/List_of_Nobel_laureates_by_coun...
The medal is not just Artur brilliance and hard work, but also due to the IMPA: http://www.impa.br/ A sixty years old institution that gathered Brazil best mathematicians and gave Artur the resources to become a great researcher. Brazil had to cultivate and invest in this institution for decades.
I am well aware of the quality of the schools in Iran and can directly compare it US schools, having gone to school in both countries. That Newsweek article is not surprising to me, but in some areas it is inaccurate in my opinion. You do see high quality individuals graduating from Sharif university, which is highlighted in the article, but concluding the school itself is "successful" or competitive is incorrect. The fact of the matter is that there is a nationwide exam to enter college level education for all schools and you basically choose your school (and major) based on your rank in that exam. In that society, engineering majors, specifically Electrical Engineering majors, tend to have high status, so if you do well, you end up going to study EE at Sharif University, probably not because you are a fan of EE or you think Sharif is any good: it just has to be better than other schools.
The outcome of this is simple: you'll have selected top N individuals from an exam of half a million people and put them in a single school. Of course you're going to see those people shine. That says _nothing_ about the absolute quality of what that school gives you, just how good it is relative to its peers in the country, and I define quality as "output - input". The "input" is high quality, but the delta is merely meh in my opinion. Also, the students are high quality--the faculty are generally not (unlike what's mentioned in the article), but they do end up taking some credit.
In terms of the contribution of the country, I can just say that she is a survivor of an accident years ago, where seven talented math students died, whom had similar achievements to hers at the time. Overall, the contribution of the country to its mathematicians has been negative, specifically so to the female ones.
I want to second the sentiment that national investment supports achievement like this. IMPA has been very important for Brazilian mathematics, bringing people from across the world to Brazil to do high-level research. This means that some Brazilians who don't have have the opportunity or desire to move to Germany or California or Korea can work with and learn from amazing mathematicians who come to them, in Brazil.
Since 1990, at least one Fields Medal winner has worked in France -- until this year. France has a culture of supporting mathematics and mathematicians. It has its quirks and difficulties, but national support for research has played an important role.
I have to correct a misstatement :( Turns out Artur Avila is now a Brazilian-French dual citizen and spends 6 months a year as a research director of CNRS. So... France wins again!
Successful people in Individually dominated professions become successful due to their own efforts. That's not just the case with Iranians, but with people every where around the world.
If some one is good enough to win Fields medal every one and every thing around works more like friction to their overall direction. And that's true for every country in the world.
I think Iran has a culture that respects mathematics and engineering and values accomplishments in those areas. Anecdotally/in my experience, there are many very good female Iranian mathematicians. (I guess I personally haven't met male Iranian mathematicians, only engineers; anecdote, as I said.)
http://www.newsweek.com/surprising-success-irans-universitie...
We don't hear about it much, but Iran has one of the best universities in the world.