I've been playing with iPhone development for a month now and I've understood the concepts and am ready to make my first app, but I haven't.
See, my first exposure to the iPhone world was through a web app my company made for its partner group. It was a simple ruby on rails web app that used my patched version of iUI to drive the experience. It was such a big hit that I'm currently finishing up a third demo branch of this for a client, hoping to convince them that even large organisations can get on the mobile bandwagon. So, you may ask, why isn't it being done as a native app? Well, there's a lot of good reasons, but what it really boils down to is that if you're writing a native app for the iPhone, you're only writing it for the iPhone.
At Mobile World Congress this week we've seen new Android devices, new Windows Mobile devices and more of the Palm Pre, devices that have one important thing in common with the iPhone, a web connection and a browser.
The best thing about all of them having a browser is that 3 of the 4 run a version of Webkit with Apple's transforms and animations built in (Windows Mobile users can download Opera ;-)) So, really, when you're creating a web app for an iPhone, you're creating a web app for all other mobile devices with a half-decent browser (S60 included).
All that said, App stores can't push web sites to your phone, which is the main source of advertising and how the iPhone apps have become so successful. Maybe Apple should allow you to browse web apps too?
iPhone Web Standards