His finances are literally discussed in the media once a week, at least. I get a channel called Management TV where 1h a day where his work and interview and lecture footage are used, called just "Warren Buffet". So 7h a week, plus the reruns. And she didn't discuss them, according to the article and to the documentary (and I happen to have watched that documentary) - she discussed how important they were to him. Which I guess anyone who has ever heard of Warren Buffet knows already. It would be like saying "Computers are the most important thing in Bill Gates's life". The world would just go "Well, duh".
As someone who was also legally adopted by a stepfather, and who was told by someone who was "Grandma" "You're not my family anymore" after a divorce, I can say that what he did there is inexcusable. You don't. People are not disposable, to be tossed after a divorce or after they misbehave. He might have cut off financially a blood grandchild too, but he wouldn't have written the "I never emotionally considered you my granddaughter" letter like he did to her. I'm curious to see if her sister paid the same price, to receive such a terrible letter for her sister's "sin" as well, or for the "capital sin" of not being blood.