The winner was Indian-American again. An article discussing why is

http://www.slate.com/articles/arts/culturebox/2010/06/why_are_indian_kids_so_good_at_spelling.html
Why Are Indian Kids So Good at Spelling?
Because they have their own minor-league spelling bee circuit.
By Ben Paynter
Slate
Posted Friday, June 1, 2012, at 10:50 AM ET

Indians do well at the National Geography Bee http://www.thehindu.com/news/international/article3456602.ece for similar reasons .

"To see what is in front of one's nose needs a constant struggle." - George Orwell