It's mostly a UK English vs. US English issue.
Oxford - closed throated shoe
Derby - open throated shoe
Balmoral - closed throated shoe
Blucher - open throated shoe
There are no differences in formality in a wholecut (Oxford) or plain cap toe (Oxford) IMO. I'd say that the plain cap toe is more for the work place (and interviews) while the wholecut is for evening wear. But for i.e. black tie events they could both be worn as long as they are in patent leather. It's more an issue of personal taste than a etiquette.