hartleymartin wrote:So this means that If I buy a brakeless fixie second-hand then it is perfectly street legal?
These rules apply only to the sale of bikes, not their use. You can modify your bike however you like after you've bought it, and the ACCC can't touch you. Use on the road is covered by state road rules instead, which AFAIK in all states require at least 1 brake. The ACCC standard is intended to protect consumers from the sale of dodgy bikes, not to specify what is or isn't appropriate for use on the road.
The reason for excluding certain types of bikes is related to this. I presume they exclude tandems and recumbents from this standard because, being written for standard upright bikes, parts of it might not be appropriate for other types of bikes, and exclude 2nd hand and custom bikes because people buying them know what they're doing.