I wouldn't have thought business that were FBO for lack of a better term were landing fee exempt. Certainly when I was flying back at Jandakot anyone that lands there paid a landing fee. Normally the landing fee is included in the cost of hire. The company I worked for charged an hour rate plus a landing fee (in the vicinity of $18 for a 4 seater).
Perhaps MB is a one off or do other aerodromes do the same?