The US has never issued exit visas. The US does not set visa requirements for Pakistan (or anywhere else).
Pakistan may have set entrance visa requirements for Americans (or Indonesians), but, as you point out, for Americans anyway the Pakistan visa was available at the airport on arrival.
Correct. The visa requirement was an entry visa INTO Pakistan by Pakistan.
Here is the source I used for this statement:
http://dosfan.lib.uic.edu/ERC/travel/cis/southasia/TA_Pakistan1981.pdf