In general, this conclusion comes from the notion that a passive house has fewer moving parts and requires less attention. A poorly insulated house demands that you take more active measures to ensure that it keeps a positive temperature (so water pipes don't freeze), this is extra pertinent should the power go out. A well-insulated house is also likely to have fewer points of failure (water getting into cracks and whatnot).

A proper passive house generally only has one maintenance point, which is the ventilation / air filtration system, and temperature control is easy. You don't have to worry much about the insides being too hot or too cold, as it should keep whatever temperature you set regardless of the weather outside.

With all that said, you should generally take everything I said with a grain of doubt, as I'm not an expert, and someone could well shoot down all my points in the comments. ;-)

My prime goal with any house I buy is to make sure that I have to do as little as possible; never worry about water being in the wrong place, and never worry about the power bill, or temperature in general.