this has been brought up many times, they say they base it on each market. In the UK for example they get a better warranty than us 7 yrs or 100,000 miles on the whole vehicle. The US 10yr/100k miles is only on the power-train (5yrs / 60,000 miles on the rest) - Canada is 5yrs / 100k km on the whole vehicle and is fully transferable. US power-train warranty is only to the first purchaser.
In Canada Kia's warranty is better than most of the other manufacturers out there like Toyota, Honda, Chev, Ford, etc. About the only one that exceeds it is Mitsubishi (10 yr / 160k km on the power-train). However, if you do a lot of driving then Mazda's warranties does not have a distance limit (3y standard, 5 yr power-train)
Back in the day, KIA and Hyundai cars fell apart in less than 3 years. They simply rapidly reached a zero growth from year to year because they were junk. The main selling point was that they were cheap but they did contain some nifty features, cheaply made but interesting. To regain some market share in the US the change in the warranty occurred to up the market share. However, in Canada, during those same years, the market did not decline there so the companies did not up the warranties.
Unfortunately i do not remember where I read that so I cannot give a citation. Sometimes i feel like my memory was made by KIA in the early days also. And yes, I owned two Excels, a four door sedan and a five door model. Both were a blast to drive, neither spent too much time on the road without some serious repairs. Cost was about 4500 each.
I'm guessing it's all dollars and cents. Hyundai and Kia know how huge the US market is and in order to stand out from others, boom, 10 year warranty = increased sales.
I'm sure their actuaries have shown this model will prove profitable. It's probably a big factor alot of us bought a Kia. It helped to sway me.
The number of vehicles taking advantage of the power train warranty in years 6 thru 10 may actually be underwritten by a third party insurer.
Some of my local dealers (even Honda) now offer a 20 year power train warranty on new car purchases. These are third party. I would imagine very few claims ever get paid by them