Apple possesses the key for most data synced with iCloud, or a huge number of iCloud features would not work. According to [1] Apple can still turn over iCloud data.
[1]: http://www.washingtonpost.com/business/technology/2014/09/17...
"This means that your data is protected from unauthorized access both while it is being transmitted to your devices and when it is stored in the cloud."
And
"iCloud Keychain encryption keys are created on your devices, and Apple can't access those keys. Only encrypted keychain data passes through Apple's servers, and Apple can't access any of the key material that could be used to decrypt that data."
And finally:
"You can choose to disable keychain recovery, which means that iCloud Keychain is kept up to date across your approved devices, but the encrypted data is not stored with Apple and cannot be recovered if all of your devices are lost."
(The last is opt-in, but seems quite explicit.)
iOS backups are/could essentially be encrypted zip archives (poor example, but you get the idea) - this doesn't require apple to have the key for it.
Is it possible to (en/de)crypt something using a password, if that password changes?