Microsoft founder Bill Gates and billionaire investor Warren Buffett are hosting an unprecedented banquet to meet China's super rich. The trip is being undertaken after 40 wealthy American families signed what they call the "Giving Pledge," a philanthropic campaign initiated by the two entrepreneurs.

But the Bill and Melinda Gates Foundation's office in China said earlier this month that some invitees to the Wednesday banquet were asking if they would be required to make donations. This prompted the two billionaires to issue a letter last week, saying the Giving Pledge drive isn't necessarily suited to every country.