I do own iWorks and I'm using iOS 5. It does work very well with Keynote on both the iPad and iPhone, but if I've stored an application in iCloud, I would expect to be able to download it to my computer from wherever I can log in, e.g., wherever I can access a web browser.
Frankly, I'd expect to be able to run it from iCloud and use it as a presentation mechanism if I chose to. If all I was going to do was store it there, I could just as easily use Dropbox, and with better results. If the presentation is, say, done in Keynote, then it is logical to assume I must own the software, therefore I should be able to expect it to "play" on iCloud. I can do that in Google Docs and with Office 365, so I consider it a significant shortcoming of iCloud that I can't do the same. At the very least, I would expect to be able to download the document to my computer to play it locally, but I see that isn't even a option.