This might cause some issues for some people who rely on this. Does this mean I can't access my Preview or TextEdit documents on Mavericks? Or is it just saying I can't browse my iCloud Drive on Mavericks?
This is why iOS 8 and Yosemite should both be released at the same time.
I doubt you'd like that. Yosemite is definitely not ready yet, lots of bugs, graphics glitches, aestheticallly looks like a mess.. Still a lot of work needed.
I think the issue is that Apple is asking users to upgrade to iCloud Drive when setting up iOS 8, which breaks iCloud compatibility with the latest Mac OS. They should have waited until Yosemite is released to deploy iCloud Drive for iOS, or at least make a .x update to Mavericks to make it work. It's also worth mentioning that the photos in the cloud feature (best iCloud Drive feature, IMO) isn't even ready with the final version of iOS 8.
10.9.5 will be out shortly....perhaps a fix?