There is a rumor talking about an Apple large screen touch screen device. It isn't an iPod touch but will be larger. An application ran on it will be backward compatible with existing touch screen products (iPhone, iPod touch). Since screen resolution are different, how can Apple solve this?
One feature that is missing during an announcement of Mac OS X Leopard (actually, Tiger) is resolution independence. Apple tries this in Leopard by letting developer to include multiple sizes of Application icon. In case that resolution independence is enable, system will pick up an appropriate icon for displaying so the icon, is shown, always sharp. It isn't as some developers expectation. The real resolution independence should be a vector rendering. Everything (includes raster images) is rendered as vector.
If an iPhone OS is resolution independence enabled, when it is deployed into a bigger screen device (assumes that width ⁄ height ratio is the same), everything should be fine. What if, the iPhone OS will support multiple windows system, since the screen is larger. Many possible things can happen!