As far as i know, Microsofts Flight Simulator games is far bigger, well, with over 10 gb's required HD space for the newer games, it's no wonder it's bigger.
And as i haven't tried the full versions of any flight sims, i don't know what it is like.
And about that FSX has about 20.000 airports around the world, i highly doubt that, but what do i know?
If this is the case, then why not something similar to ship sim?
And yes, i know ports in SS looks different.
One last thing: The bigger, the better (for some things).