Hmm that page is pretty unclear. Because while it says the data is encrypted serverside. What it doesn't say is which data is encrypted with a key that Apple has access to.

Much of the data listed as encrypted on server is available to US law enforcement under warrant.

It would be nice, to have an option available where data is encrypted on server, with your key. But that would mean you couldn't recover your data if you lost your key of course (and I think Apple consider that a poor user experience, or are under pressure not to do that...).