That's somewhat dependant on the locality and the type of code but you're generally correct. Some communities require upgrades only at the time of sale, while others grandfather older codes. Certainly, it would not be cost-effective to bring an older mobile home up to newer standards. The things are very modular and would require a complete rebuilding. Its cheaper to just make a new one.
That said, I'm still a little less than enthusiastic about the government getting too overbearing in terms of construction. We can build an absolutely hurricane-proof structure, up to catagory 5, but it would be enormously expensive. Few would be able to afford it.
Housing needs to be available at all levels - cheap, middle class, and upper class. And the market generally takes care of this. We have to be careful not to let the government price low-cost housing out of existance. If I had but $5000 in my pocket and a low-wage job, I'd not hesitate to buy a trailer to live in. I'd take that over any government-subsidized housing any day.
BTW, I wasn't picking on your post - just speaking in general, since I have the floor for a minute.
When a fantatic and unusual bridge is being built a factor is added for loss of workers in construction. Same with skyscrapers. Do we quit building bridges and skyscrapers?
Remember everybody had time to leave and was warned. If people stayed in a mobile home with a 145 mph hurricane coming, they were, sadly, very stupid.