For example, the pronunciation of "priv-" in the words privacy and private is different in British English. The former is pronounced as prɪv- whereas the latter as praɪv-. Yet, in the US, the pronunciation is the same.
Meanwhile, the word privilege is, so far as I know, pronounced the same in both British and American English (prɪv-).
There seems to be something very arbitrary in all this. But there must be an explanation. Any ideas?