That was my suspicion as well, but just on the basis that for certain features such as the keychain they do explicitly talk about how the encryption works and having no access at Apple, so maybe the exception proves the rule. However, I've also read in several places that Apple has been at least considering reworking iCloud so that it really does have no access, as a means of countering government prying eyes. It would be nice to get the current facts, whatever they are.