That enables a lot of app-specific features to be universally applied. Since Apple is making the APIs for iCloud storage and sync available to all its developers, it should offer an impressive editing experience from iPhone to iPad to Mac or PC and back (assuming the app has a Mac/Windows counterpart). It should allow data and document access to be seamless. And with the sync capabilities of iCloud baked in, it should also be effortless ; there's no need to move a file using some other app or a clunky Web-based upload form.
On the other hand, your actual access to documents becomes more limited. You need to have specific apps on each device and you need to access your stored documents using Apple's solutions. In other words, it's a more closed system.
Two approaches, one goal
The interesting thing is that both Apple's app-based approach and Google's Web-centric mindset point in the same direction: instant access to your data, whenever you want it, wherever you are.
But the core values about what's important in achieving that goal are radically different and that leads to vastly different experiences. Apple is focused on keeping the experience of viewing and working with documents and data the same while providing ubiquitous access from a smaller set of solutions. Google wants to make your documents and data available from the widest possible array of sources, with the expectation that your hands-on experience may vary greatly from one device or app to the next.
You can criticize either approach for the tradeoffs made to achieve those core values. Apple does keep you in a walled garden. Google doesn't deliver a seamless and effortless experience.
The truth is that neither company is entirely right or wrong. Each is simply showing what it believes is most important to users, and it'll be up to the users to choose which cloud approach we prefer. That will vary, depending on what types of data you work with and how you want to work with it.
Perhaps, iOS users will have one advantage: they aren't limited to iCloud. I have no doubt that some of my favorite iOS apps, such as QuickOffice, will adopt Apple's iCloud APIs. That won't prevent them from accessing Google Docs, Dropbox or other cloud services. In other words, while iCloud will become an option for me on my iPad and iPhone, I won't be limited to it.
On the other hand, I won't have access to iCloud -- or some other solution fundamentally baked into the OS -- on my Android phone, even if I wanted it.