I've had my EX limited now for about 4 months with the Hankooks on it. My tires have only been in hot weather (very hot) but have worked very well with no wear issues or strange handling of the truck. In a perfect world, I wish they were American tires, and unclear why Ford picked Hankooks vs something else.
Just for the record, your EX is 85% american parts, designed by americans and backed by an american company were the profits go into community. There are very few vehicles that are more amercian than the 2011 Explorer.
Of all the post I have read in the forum in the last 4 or 5 months, I can't remember one that talked about the Hankooks early wear issues on an Explorer, or poor handling characteristics or failure of a tire. You will find that people on the forum are not shy; if they had tire issues, there is not a lack of energy to describe them in infinite detail.
So for me, whether I have Korean tires (Hankooks), French tires (Michelin), Japanese tires (Firestone/Bridgestone) or American tires (Goodyear) is a personal choice. Changing tires, for me, is not backed up by data on Explorers that I have seen.