So much of this hinges on how easy it is for developers to support all the different display sizes.
At the moment you need to design for 640x960 and 640x1136. For most apps that's more work than most people realize. Then you also want to support iPad, which is both a different resolution and different aspect ratio. That's the big reason you don't see more apps with native iPad support; it's too much trouble to redesign everything.
Now add two more display sizes into the mix.
This isn't just about whether or not people want bigger phones. It's about whether developers can design beautiful apps--and redesign all of their already released apps--for those phones.
At the moment you need to design for 640x960 and 640x1136. For most apps that's more work than most people realize. Then you also want to support iPad, which is both a different resolution and different aspect ratio. That's the big reason you don't see more apps with native iPad support; it's too much trouble to redesign everything.
Now add two more display sizes into the mix.
This isn't just about whether or not people want bigger phones. It's about whether developers can design beautiful apps--and redesign all of their already released apps--for those phones.