It's no consequence that many think the iPad looks like a really big iPhone. It's basically the same look and feel working about the same way. This has led many to wonder if iPhone applications will run in the iPad device. The answer is yes they will.
The iPad uses a very similar platform or operating system as the iPhone. They are very similar devices except the tablet is obviously much more powerful of a device and has a much larger screen. From day one applications from the iPhone will work on this new device.
The next question many have is how these applications are going to look on a much larger screen. Are they going to be a in a small box or are they going to fill the entire screen?
The iPad will be able to do both of these functions. The application will launch in the center of the device with the same size as it is on the iPhone. There is a small button on the bottom right that will let users make the application fill the entire screen. The pixels will be a bit bigger meaning the picture won't be as clear, but at least it will fit the entire screen.
While some applications might be useful especially at first where there won't be as many, it's only a matter of time that many of your loved applications will be replaced with iPad ones made for the larger screen. Also many won't be needed because you can just use them as normal in the web browser like Facebook for example instead of having to use a smaller iPhone version.