There are any number of modifications people can make to cars that make them more dangerous through no fault to the maker. On some cars, not making modifications is something of an exception, think of Wranglers.

The difference I think is that if someone modifies their jeep and ends up killing themself, it is rather easy for Jeep to prove their innocence; no matter how wrecked the car is the modified suspension or whatever will still be rather apparent. Imagine the nightmare that would be for a software company though.

Of course proving innocence is not how things are supposed to work, but...