no, that's not true, there is definitely a lot of bikes out there with cats in them. i know for sure that both the ducati monster s4r and 620 have cats from the factory because mum and dad replaced the exhausts in theirs.
zx-14 does seem to be a very good engine, dad has one and not that he'd know but it does 180kp/h in 2nd gear with standard everything except the secondary throttle bodies removed or something like that and yoshi slip ons. i'm not sure what gearing you'd use for a car, the zx-14 is speed limited to 300kp/h but i'm not sure if the motor would push a car to those speeds?