Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
From a technical standpoint, it should be really easy to update for iPhone 5. At our company, it was simply recompiling the source code. Then just a few minor tweaks to art assets. But even for fairly complex apps, it should be more than a couple of days work to get everything running beautifully. If we have to wait more than a month to get major apps updated for iPhone 5, then it is just lazy developers.
 
From a technical standpoint, it should be really easy to update for iPhone 5. At our company, it was simply recompiling the source code. Then just a few minor tweaks to art assets. But even for fairly complex apps, it should be more than a couple of days work to get everything running beautifully. If we have to wait more than a month to get major apps updated for iPhone 5, then it is just lazy developers.

Games will take much longer. And it really depends on the design of the app and the amount of resources you have available to put into updating. Considering Apple didn't provide any lead time for updating your app, developers may not have had updating on their schedule.
 
Some developers might just introduce new apps rather than update, but most will update for the new screen. Otherwise I think users will avoid those apps. I know I have gotten spoiled by the apps that are upgraded and have stayed away from the ones that haven't.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.