Departure calls are extremely useful where there is significant terrain shielding - YSHR is a classic example - taxi calls cannot be heard by aircraft inbound from certain directions, inbound calls from aircraft arriving from certain directions cannot be heard by taxiing aircraft.
Confusion on which rule applies - there should be none. Anything in the CAR's is a legal requirement. Nothing in the AIP is a legal requirement unless specific provision has been made for it to be a legal requirement in the CAR's.
As far as I am aware, the the only calls legally required to made by a non rpt aircraft are: inbound to a CTAF(R), inbound intending to make a straight in approach, prior to entering a runway at a CTAF(R), and in the vicinity of of a CTAF(R). In the vicinity of an aerodrome is specified in the CARs as 10nm and at a height that could result in conflict with aerodrome traffic. The above are what the CAR's legally require. Any other calls are only "recommended" by the AIP - such as taxiing, turning in or entering the circuit, 3nm and 1nm.
Likewise the requirement for turning crosswind - the only legal requirement that I am aware of is the requirement to climb to 500 feet above ground level unless you require to turn earlier for terrain avoidance or are taking off from water (seaplanes have an exemption). The climb to within 300 feet of circuit height is only "recommended" by the AIP.
Before I get flamed, I am not suggesting to ignore recommended procedures just because they cannot legally be enforced. However there are numerous occasions where the safest option does not include complying the the recommended procedure. Choosing when to follow and when not to follow recommended procedures is command judgment. Recognizing that a pilot may do so is essential for safe aviation rather than blindly following 'recommended' procedures.
JM
to the last post
PS I am happy to be corrected on legalities - references to Regs to be included please.