Originally Posted by
AA_EXP09
Typically, clearning immigration means reclearing security for a domestic flight in almost every major airport.
It's the same thing in the USA, Canada, HK, TPE, ICN, NRT...
(even international to international clears security for these airports.)
That just goes back to first principles everywhere: If you have arrived from another country, you must be re-screened to local standards before you depart on another flight.
Situations where you don't get re-screened are exceptions to the basic principle.
If you have to clear immigration, then by definition you have arrived from another country, thus triggering the basic principle.