Buffett isn't all that nice. His grand daughter did an interview in "The One Percent," a documentary created by Jamie Johnson, the heir to Johnson & Johnson about the growing wealth gap in America and how the top one percent controls 40%+ of the nation's wealth.
After Buffett's grand daughter interviewed in it, he disowned her from the family. Wrote her a letter saying she wasn't his grand daughter anymore and that she wasn't part of the family. She even showed the letter on film and there was an article about it in the NY Times.
I don't know why someone that lives so modestly would have a problem with their grand daughter talking about how she believes the ultra-rich have too much money.