Everything is rated for the locality of the service....whether you buy it across state lines or not, you are going to pay the rates for the locality in which you use the services. The only logic that "buying across state lines" makes is the ability to buy a plan in a state that lowers mandates.
So, let's say that an OK based insurer sells a product without all of those NY mandates, but prices it for NY zipcodes. The premium would be less for New Yorkers, because there are fewer benefits mandated.
It also brings adverse selection to a national scale. So, let's say that one NY family chooses Oklahoma-based insurance (rated for their NY zip code) because the mandates are the least. The next NY family, with a special medical condition, picks coverage from another state that happens to mandate benefits for that condition. Bingo - adverse selection.
So, then, why would any carrier sell IFP from any state other than the one with the fewest mandates? It's a great race to the bottom.
Buying Across State Lines - pt 1
Buying Across State Lines - pt2