Which is exactly what a lot of users will be unable to do. They'll rather avoid the hassle by buying a new Apple device yet again.
I'm not pointing my finger at Apple per se. If they provide a reasonably user-friendly way of moving your data then it's hard to blame them. But the fact is that most people will want to avoid the hassle, which means the iCloud becomes a lock-in mechanism.
However, if an app doesn't provide either that or some kind of export, I'm not sure if you'd get easy access to that data. And actually that might create an incentive for some apps not to add the functionality. It makes sense for Office-type apps to provide a PDF, or Office-compatible format, but I could imagine very specific apps that can lock you in since you don't get to (easily) reverse-engineer and convert their data because you don't get as easy of an access as you get on a desktop.
Don't ask me, ask Apple - they're the ones who're doing it :) Contacts was one of the things that Apple mentioned would be stored in iCloud at their talk a couple of ago. I'm not sure about email.
One of the reasons your contacts would be stored in iCloud is so that they can work with Apple's (proprietary) new chat/message system; iMessages.