True it can show that, but outside of chainfires explaination of how it is blown and "what has been hearing about Samsung service centers". If you read his article, there is a lot of maybes, mights, and even ends his article with "take it with a grain of salt".
Their are a lot of mad people in his chat, but I didn't find anyone saying they got denied. Samsung can do what they want, but they know word of mouth is as big as advertising is. One person saying "I installed a program, it broke is my phone and Samsung is not honoring the warranty" has a huge impact on people regardless if they know and/or understand rooting.
Knox security void can mean the phone can no longer be certified for enterprise grade applications or environments. That the security mechanism is tainted thus considered broke and not repairable.
Just my point of view - I have total respect for chain fire
Edit: Additional info
The Magnuson-Moss Warranty Act (1975) says that to refuse warranty, the company must prove that the problem with phone (or any other device that fails) was the caused by the customer.
So a defective sim card reader (unless obviously damaged by a consumer) should be covered where a modified corrupted partition table causing a boot failure (and also not a wide spread incident) may not be covered as this is more of a damage from a "non-friendly" application caused by the consumer.
Samsung Galaxy s4 - 64 Gig Sandisk
(Yes I had an iPhone)