Sosouth:
Maybe Piper, Cessna & Beech (piston) stayed away because Cirrus, Diamond and Airvan are the big sellers and the show is not worth it (too expensive to display) if no sales result.
Cessna sells steady numbers but it's been a while since Piper or Beech have sold anything new here.
As for QF, DJ etc.
Jetstar had a display and I don't think QF would want to take the gloss off little brother by having a display. Also, having Jetstar RPT arr. & dep. during the show was a marketing coup.
Why would DJ waste money on a display - in an area they don't service - when Jetstar steels the limelight several times a day.