Hacker News Reader

The two reasons why you would want to use the Objective C iPhone SDK are:

access to advanced multi-touch gestures, the ability to store data on the iPhone.

If your app is simple, though, a web application running in Safari might be a feasible solution.

High-performance applications? 3D? Accelerometer usage? Access to data on the iPhone (contact list and such)?

Also, push notifications, in app purchases, simply being able to generate a second revenue stream...