Yeah, this article badly misunderstands what iCloud is for.
First, it's a backup service for iOS devices that eliminates the need to sync them with with a computer, effectively untethering iOS devices. And yes, if an app stores PDFs, images, movies, whatever, within its data store, iCloud will back them up. Once your iOS device is backed up to iCloud, if you happen to drop it in the ocean, you can go buy a new one, sync it to iCloud, and all of your stuff (with the exception of non-iTunes music if you don't have the $25/year iTunes Match) will simply come back.
Geeks like us have trouble understanding the value of a service like this to average end users, but it's huge. Most consumers, to this day, still don't have backups of any kind, and virtually none have off-site backups. Apple reportedly had lots of people coming into Apple stores who hadn't synced their iOS devices since first setting them up, and would therefore lose considerable amounts of data if device replacement was required. iCloud simply makes these problems go away for people. It makes off-site backups simply happen by default, rather than requiring the user to understand the importance of them and go out of his/her way to make them happen.
Secondly, iCloud a seamless sync service designed to be integrated into apps. With an iCloud-enabled version of Pages or another iWork apps, you can be working on a document on your Mac, grab your iPad and run out the door, and keep working on that document there -- even if you didn't explicitly save your most recent changes. You can add a reminder in the new Reminders app on your iPad, and seconds later it will also show up in the equivalent app on your iPhone. You can start playing a game on your iPhone, and your progress can be seamlessly synced to your iPad, so you can keep playing there from exactly where you left off. Third-party developers can add features like this to their apps using a trivially simple API, with no need to own/rent their own cloud infrastructure or write a single line of server-side code.
Comparing iCloud to Dropbox doesn't really make a ton of sense. The services are designed to do very different things. The only real overlap is in the instance of things like syncing iWork documents... but even there, the approach is conceptually different. Dropbox is "a folder that syncs" iCloud is a data sync service intended to be integrated by developers.
Describing iCloud as "underwhelming" is effectively a compliment to Apple. It's supposed to be invisible. A decade from now, non-savvy users will simply take it for granted that their data is magically propagated between their devices, and it won't even occur to them to think about the mechanism through which this occurs.