Odd. They are extremely common in California. My office mate has one, her second after giving the first to her daughter. A friend has a motorcycle accident and TWO Prius were involved.
So in the USA, or at least in California they are very common. Part of their popularity is their fleet use makes them direct cheap in the used market, and they tend to be pretty reliable despite the complexity of two separate drive trains.
I think one of the issues is that the Prius starts from $30,000 here - which is quite a lot - and a lot of cheaper, but still economical cars are available for much less.