I was reading an interesting post a few days ago that argued that a big reason for the popularity of App Store apps on the iPhone is how hard it is to use web apps on that device. Make no mistake, Safari on the iPhone is a very good browser, and the iPhone is a very good web environment. However, it's almost always easier to use a dedicated iPhone app than a web app.
The iPad may change that equation. The iPad's bigger screen size, bigger on-screen keyboard and better performance should make web apps much more viable on that platform. Web apps can be written in far more languages than iPad apps, they should work on multiple platforms (so long as they're not written in Flash), and they don't need to go through the App Store approval process. There will undoubtedly be a healthy market for native iPad apps, and I'm in no way against native apps. However, I believe that web apps will work much better on the iPad than on the iPhone or iPod touch, and you're going to see a lot of them.