The ERP is the Effective isotropic Radiated Power, or in other words, the amount of power that would be required to produce a uniform spherical radiation pattern having the same magnitude as that of the peak of a non-isotropic or directional radiation pattern. TV antennas are just big dipoles, and the radiation pattern looks something like a doughnut. They don't waste power radiating straight up into the atmosphere or down into the ground below the antenna. The ratio of actual radiated power to EIRP for a dipole is something like 1/20, so you would adjust the FCC ERP numbers down accordingly before adding transmitter inefficiency back in.

And then, of course, the refrigerator comes on while you simultaneously blow dry your hair, vacuum the floors, and watch your 60" HDTV. In other words, I completely agree with your point. 200A service should be overkill for just about anything shy of a mansion or a family of 12. You would have to live in a part of the country with very cheap electricity to have all of your major appliances be electric in the first place. Though, as with too many things in life, you have to regulate for the lowest common denominator. Plan for the worst and hope for the best, etc.