The context of 101.075 is operations near aerodromes, and subsection (1) refers to ops above 400FT within 3NM of an aerodrome.
There is no need to say "and" 3NM. It should be read as it is stated.
Imagine two volumes within 3NM; one SFC-400FT and the other above 400FT, and its this latter volume that is covered by 101.075
Part 101.085 covers all unmanned aircraft i.e. UAS, model aircraft, rockets, unmanned balloons etc. etc.
101.400 is specific to model aircraft, and its my understanding that model aircraft in populous areas are normally restricted to operating in areas approved by CASA, unless the location is away from populous areas, in which case it is enabled by 101.400 - and 101.085 (b) is the link for that.