The difference id that in the US the FAA is funded from the public purse wheras the CAA must cover all of its costs in fees as it gets no funding from the government.
If you consider the case of exams, if you choose to sit these at a remote (from Aviation House) venue the CAA has to pay someone for the rental of the exam hall, pay for the invigilators, costs of marking etc etc.
The overheads on the Belgrano cant be cheap either.
But I do agree its a lot of money. Make sure you go and have luinch in their canteen one day and recoup a fraction of what you've paid in.
I think I paid the CAA the best part of 4 grand to get my CPL/IR with frozen ATPL.