Warren Buffet's Philanthropy Philosophy

In his letter about philanthropy viewable on http://givingpledge.org, Buffet outlines what he thinks of philanthropy and volunteer work.  Buffet says that philanthropy means a lot more when people donate and that those donations are a sacrifice.  In other words, those whose donations cause them to miss out on something (i.e. a movie, a dinner at a restaurant etc.) are donating a lot more than Buffet will when he donates 99% of his wealth to philanthropy.  Buffet explains his opinion that time is worth more than money (he uses the example of mentoring a struggling individual being worth more than giving them money).  While I am impressed by Buffet's commitment to philanthropy when compared to that of others from a dollar standpoint, I agree with him on the point that volunteering one's time is a greater gift than that of donating money despite the idea that, "time is money," not so when it comes to philanthropy.  Buffet says that, "Nothing will go to endowments; I want the money spent on current needs," but I wonder what his kids think of this.  Obviously I'd expect them to be successful in their own right with a father like Warren Buffet, however, I'm curious to know if they perhaps feel cheated out of something that they felt was rightfully theirs even though they, as Buffet notes, "live comfortable and productive lives," and have already received large sums of money.  Near the end of his letter, Buffet expresses the idea that, "too often, a vast collection of possessions ends up possessing its owner," and this is an idea that, while I don't have experience with, seems reasonable and a bit of a jab at most other wealthy people who own several residences and other exorbitant items.  Buffet concludes his letter by explaining that he donates his wealth from gratitude, as a way of giving back.  That the 99% of his wealth that will be donated to charity and other philanthropic organizations isn't something he will miss and that using that money for anything besides helping the health and welfare of others would be rather lame.