All the belts are the same.  I don't have an official explanation as to why
this is, but I suspect it's a legal issue particular to California where
they cannot force you to replace the belt to maintain the warranty.  If
you read the manual, it'll say something like "recommended but not
required."  The *recommended* interval for your vehicle is 4 years/60k
miles, regardless of where it's been purchased or where it's registered.

Furthermore, I believe the state of registration is what they're talking
about.  You should be able to get clarification from Hyundai customer
assistance on this.

As far as your timing belt goes, you should be concerned about breakage or
strippage.  You're in the 6 to 7 year range.  I've seen belts on Elantras
like yours strip at this age.  Remember, the recommended interval was 4
years.

In any event, if your car is registered in California (or Hyundai tells
you that you have some other connection with California that makes it okay
not to change the belt), you need to consider whether the cost of the belt
is worth the trade-off of having your car in the shop for a significant
period of time for engine repair in the event the belt breaks.  I don't
think this belt will last ten years.