I read the US consumeraffairs.com page on Kia, which was very long. And then I decided to try their pages on Nissan, Toyota, and the like. What I found was there were pages that were just as long for those makes - except in the case of Nissan and Toyota, the pages were for a single model (Maxima, Camry) etc. as opposed to all of Kia. Also those were concentrated on a couple of model years, whereas the complaints about Kias stretch back to cars that are 8 or 9 years old (some dude talking about his transmission that failed after 140k miles etc).
There's lots of cars in the US, a different driving style, and a lot of crappy drivers. I would not worry about it too much and take most of it with a grain of salt - haven't heard it happen in SL as yet, and there's a 100k KM warranty on Sorentos in SL if it does happen.