I just noticed that there are three screen sizes for touchscreen iDevices. The iPod Touch's, iPhone 4's, and iPad's. Isn't this putting increased burden upon app makers? Just wondering.
Not really, because everything scales pretty easily. Plus, like the interfaces, they're designed to switch depending on device.
You can choose between iPhone and iPad. And if you've ever worked with Interface Builder, you'll see that when you add navigation, tab bars, etc, it automatically adjusts the width.