For understanding purposes, think car is just like any other machine. It can be dead, broken, fail, could be anything. It can happen to ANY CAR not just Prius. Most cars fail because of the drivers/owners. Who do not take care of their cars. Or at least do not understand their car.
I hope you must have heard the CNG kit does not work with many Japanese models. You know why?.... Because we the drivers do not know our cars. For your information most Japanese vehicles have CVT (continuous variable transmission). CVT does not have a fixed number of gears, like any other conventional 4,5,6 speed auto transmission. CVT has unlimited gears. CVT was developed for better fuel efficiency. Ask your friends and family members who own a Japanese vehicle, about the transmission type in their vehicles? 90% of them will tell you its Auto but they won't know the type. It proves again that owners do not know about their cars.
Now as far Prius goes. it is an excellent choice. More than 4 million cars have been sold worldwide. Without any special failure incident such as batteries, or engine. Guys, go ahead if you want to buy the car go get it. World has gone beyond the Hybrid, there are electric vehicles.
There are several types of consumers;
Early adopters.....
Early Majority.....
Late Majority.....
Laggards..... (most people going against or opposing Prius fall into this category).
Cheers....