I would be willing to bet that the majority of Hyundai's will out-last their 100k otherwise why would a company be willing to make that bet (except that most cars stay with their original owners about 4 years)?
The Hyundai 10 year - 100K mile extended drivetrain warranty was started back in 1998 for the USA market back when Hyundai reliability was very sketchy (and no where near as good as it is today). It was necessary due to the very poor reputation that Hyundai had going back to 1986 when they first started selling the Hyundai Excel in the USA. The only thing that saved Hyundai in the USA market was that there was an even worse car imported in the same time frame called the Yugo (made in Communist Yugoslavia).
Even recently, Hyundai Motor America has noticed that a significant number of Accord and Camry buyers don't even test drive a Sonata due to Hyundai's reputation problems going back a few decades ago. Fortunately, that is changed as younger buyers don't know anything about Hyundai's past reliability problems. But the extended drivetrain warranty is designed to help alleviate the fears that customers may have about Hyundai reliability.
Many people mistakenly believe that warranties are determined solely by engineers based on how long they think the product will last. In fact, warranties are primarily determined by marketing people, and warranty expense is considered a marketing expense, and tailored to each individual market, both for competitive reasons, and also for regulatory reasons. Even today, the extended drivetrain warranty is
only available in the USA market by Hyundai Motor America (not offered in Canada or any other market).
Of course, once Hyundai Motor America starting offering the extended drivetrain warranty in the USA, it did put pressure on the engineering staff to make vehicles more reliable, but the marketing was the driving force. And as you stated, most people don't keep new cars for 10 years or 100K miles, so that that lets Hyundai off the hook on most vehicles.
One interesting fact is that Lexus and Acura have slightly longer warranties than Toyota and Honda counterparts. I don't think Lexus and Acura are more reliable than Toyota and Honda (especially for the vehicles that are very similar to the luxury branded ones), but it is just an extra warranty duration that is built into the price of the cars because they want to give the impression that the luxury branded vehicles are more reliable.