Remember when people predicted videoconferencing would kill the airlines? For better or for worse, it hasn't, and business air travel continues to increase (despite doom and gloom predictions of our supposedly shattering economy). There's just no substitute for being at a meeting, making a live presentation, or simply shaking your client's hand in person. Airlines allow you to shake people's hands in 10 cities per week (though it'd be the week from hell), whereas a long-distance train might let you shake one or two.