Yes. There is a decent change when dealing with new screen sizes. People did not know the new screen resolution until Apple's announcement.
It is not as simple as stretching an app. You need to worry about the new size of your icons, buttons, pictures and such within the app, and if you want to properly use the extra screen space for productivity, it requires a possible redesign of the app.
I also want to echo Dan's comments, because he is 100% right. Serious app developers test their apps on the new phones, which just came out. Slower developers are on a waiting list for the phone waiting 3-4 weeks for shipment because the phone is so popular. Until they get the phone in their hands, they cannot properly test the new version of their app
This is the _second business day the new phone has been available_. I feel like the massive rush of apps with updates today is an amazing testament to the super-fast response time of iOS developers.
It is one part for the developers to edit their code for the new screen, the other part is the Apple Review process, which can take a while.
They are starting to come along. Netflix updated today so videos are now in full widescreen. Games are going to have the hardest (longest) time updating as they will have to adjust art and scale.
Dare I say it ? Fragmentation anyone ?