While it is true that the individual machines can sync with Google, iCloud cannot directly.
The reality is that while iCloud may be an excellent system for linking Apple products the truth is that Google Apps are available on more platforms. Just like Apple systems can deal with almost any file system, Apple's iCloud should be able to sync with Google calanders and address book. Many companies and schools use Google services for shared calendars and resources. It would sure make sense to provide that as an additional service as well. It wouldn't be any harder than implementing the sync and delegation methods already implemented in the standalone apps on the platforms.