I read somewhere that Warren Buffet too flies coach in the USA but am not sure what was the source.
Closer home, I once sat next to the an elderly British gent on the flight from KL to Singapore in economy class. That was in the late 70s.
He was the owner of the Boh tea plantations in Cameron Hghlands; a Mr Tristan Russell.
It seems that some wealthy people know how to preserve their monies. After all, the trip from KL to Singapore or Penang takes about an hour so why pay three times for a seat on the flight?