My five Cents: At my Option, PMDG wants to sow their Deepment of the Systems but they are new to X-Plane Developement. They want to make an Plane with an Custom FMC but not to much Systems like FBW etc. The 747-400 is an pretty old Plane but it's great in FSX and the MD-11. The MD-11 is a bit newer than the 747 ( Developed for FSX) . Then to the Little Aircrafts: Popularity: People buy the Aircrafts they see and fly in Real Life (The most time) YOu see the B1900 often in the USA but in Europa, they are really rare!