How does pgAdmin III build CREATE statements?
pgadmin has it's own reverse-engineering functionality - it just examines the system tables like pg_class and pg_attribute to find the details.

If what you're looking for is actually an easy way to show the CREATE statements for your objects that you can use from something else, you should look at pg_dump instead of pgadmin, it is much simpler. In particular, if you just want to look at it for one or more object, you can use pg_dump -s -t tablename and it will give you the required CREATE statements.