Nathan,
in fairness, Oxford do cut loose very very few students...I think it's in the region of about 6-10 per year, from all phases.
However, Oxford have a scheme whereby if you "can't/don't" make the grade all the way up to the CPL exam (I think it is - it fairly recently changed from PT1 - effectively the PPL skills test) they will refund your costs of training (I think minus the ATPL theory costs), so actually the worst you lose is about £4.5k for the theory and the time out you've taken to progress to whatever point. Hence why they try and ensure that everyone has the aptitude before embarking on the course - I'm sure they don't want to be writing refund cheques too often!