well... I've already been buying my apps for 3 years so I've basically already accumulated (most) all the apps I will need. There isn't really much chance I'll buy any more apps between now and iOS 5 is released anyway. But If I did I wouldn't worry about it a whole lot, because I'm only going to purchase apps from devs who actually care about and support their app. And those devs will be adding iCloud support most likely.
I'm hoping all the apps I already have give iCloud support.
Which leads me to my next thought. How long do you think a successful app will be supported before the dev says "Ok you've got your x.99 worth" and stops updating it. then makes a new app and starts adding features there. Or would it just be easier to add certain features through in-app purchases...