Would it be safe to assume that there exists, car seats for babies and children that are not safe for use? Certainly anything is better than no capsule or booster seat at all. All in all, I think we're exaggerating the big picture which is why I don't think insurance companies would make such a big fuss.
I hate to bring the discussion of car compliance but the analogy is similar to the topic of discussion. There does exist a higher standard abroad than the safety standards in NZ. Good example is the US car crash safety requirement. For the longest time, NZ was able to use cheap 2nd hand Japanese cars from Japan which where an inferior standard to the US requirement. These cars were produced for the 'domestic' japanese market with no intention of being used overseas, but many of them get shipped over to NZ and meeting NZ safety standard. Actually, I should say it wasn't until recent years where NZ had lifted the standard which made a certain years of Japanese cars not able to be registered for NZ use, but several years too late compared to the US requirement.
A good example is my uncle's 98' Corvette. It was imported about 6 years ago having seat belts of a different type. Upon registration inspection, the inspector told us, "This method of seat belt restraint
super cedes the NZ standard". To give you an idea, virtually all passenger car seat belts use the locking restraint across the chest (the belt that crosses diagonally locks up in an accident - when WOF test it, they give the belt a tug to see if it locks). In the Corvette, not only the diagonal belt can lock up but also the belt that goes across the person's belly or belt. Other safety features the car had at the time was traction and stability control. Again, only recent TV ads where NZLTA started marketing which cars have this feature today and highly recommend it.
Overall, I still find it very hard to believe US safety standards are "bottom rung". It can't be with a population of over 300 million.