Body language is a huge factor in communications. That's why email is a really bad way to do performance reviews, etc. Unless you can read the other person's body language to go with their words, you're missing out on more than 1/2 the conversation - literally. (http://en.wikipedia.org/wiki/Body_language) Plus there is the added relationship-building that only happens face-to-face.

I just don't see the author's prediction coming true for any line of work involving a customer relationship, whether the customers are internal or external.