I might be rewording what a few people have said already.

There is a theory, and if I understand it properly, it says that heavier wheels (and bike) will slow you down compared with light wheels, but over long distances, the difference can shrink depending on your pace, conditioning, and terrain. Add to that the fact that softer tires have the potential to reduce rider fatigue, and the result has the potential to require less energy from the rider to cover a given distance at a given pace with the fatter but heavier wheels. I don't know if this has been tested and proven, but Jan Heine is building the data and evidence. In time, he may be proven wrong, but a lot of happiness is spreading among those who are trying fatter tires in 700c and 650b.