Several of the Oracle of Omaha's longtime favorites would be at home in most investors' portfolios. It's not nearly as surprising as it may seem at first glance. See, while American Express is frequently lumped together with Visa and Mastercard (for obvious reasons), it's not quite an apples-to-apples comparison. Its business could be better described as a marketing and rewards program that just happens to be centered around a card payments network. Its card holders are willing to pay as much as $700 per ye ...