The reality is that unless and until someone makes a very specific complaint about an issue - preferably drafted by a lawyer, with each paragraph beginning with the word "Wherefore..." - the ACCC will keep sending form letters in reply.
Let's strip away all the technical aspects of the issue and the noise and focus on just one thing - whom can Microsoft claim it is protecting by insisting on a secure boot process? Why, the consumer, of course.
Incidentally, the ACCC's mission is also to protect consumers. Does one then expect the ACCC to act against this measure when there have been reams and reams written about the malware problem that Windows poses?
Rest here 
Also: That Whole Windows 8 Secure Boot Ruckus