The Castello Brothers are a class act and I respect what they have accomplished. It's even more gratifying to see their openness toward other geo domain owners and their willingness to share information.
In my view, the geo .com's will remain at the very top ... that position is locked in. But the alternative geo's in tv/us, etc. can be very valuable in the long haul and provide a range of different services and audience value that compliment the .com equivalents. In fact, successful cities in any of the major extensions likely build on one another drawing attention, and money, to the geo niche.