Sure. The thing with the Gates Foundation is that it was able to handle billions. Most charities aren't equipped to effectively manage and deploy that kind of wealth. The Gates Foundation made it easy for billionaires to send a large lump sum to one place that was equipped to deal with it.

Having to part out all his wealth $5m at a time to spread it around without overwhelming the systems in place, would be a second act that I'm not sure Buffett has the time for.