It's not an open cloud. I wasn't aware there was a strict definition.
But the general point of people providing online service based applications is that from many front ends they have one back end. Having it locked down to a platform is utterly utterly pointless and pathetically purposefully divisive.
I really am quite sure the future of modern global interpersonal communications is utterly disastrous given the state of rival networks fighting it out instead of working towards inter-operable-fault-tolerant-distributed-vendor-agnostic solutions.
Email is still the best way of doing this but as Instant Messaging has shown for the past 20 years (no standard ever caught on) without that we end up unable to communicate reliably and one logical place with everyone. The only thing even close has been SMS.
I can't resist slightly getting into it: it was a perfectly decent metaphor until some marketing numbskull heard a technical person use it and decided to stretch it in ways that made it meaningless.
Back when it simply meant, "look, you push your packets into the network and a bunch of routers decide how to get it to its destination without you having to worry about routing" it was fine.
But as a metaphor: I think Jon Postel might have been the first person I heard use the term. I also feel like there was such a picture in some of the early IP documents (like the internet protocol transition handbook in the early 80s) but that stuff I had on paper and it's stuck in a box someplace.
Regardless, it's been horribly abused by marketing people and does need to be dragged out back and put down.
What APIs do the iCloud.com web-apps use, then? ("Non-public ones" is the likely answer.)
How to monetize the user is still wide open, but Apple will be covering the storage and server tab. (With money added from heavy users. Casual users needn't pay.)
The dark side of this is that there doesn't appear to be a way for a browser or non-Apple product to interact with the stored data. So you trade free backend servers for writing software only for Apple customers and even then not when they sit down at a borrowed machine.