The course manuals (not just Oxford's) are written to give you a reasonably full understanding of the subject at hand. The examinations are intended to check that your understanding is sound. For fairly obvious reasons exams cannot ever test all of your knowledge and the idiosyncratic style of the CAA seems often to be testing your understanding of the CAA's version of English rather than the subject, but that's not Oxford's fault!
What they and most schools try and do is to give you the knowledge then use the question banks to apply the knowledge in the way the CAA wants it done.
Scroggs