There always seems to be a push from IT folks to cross-develop for multiple mobile platforms. The truth is, in many cases you just cannot make a mobile application that is quite as compelling as a native app. You lose a lot of the hardware access and speed that make it so satisfying to use something like an iPhone application. That is why you see people like Facebook making apps for every device. In addition, you lose the app store exposure and marketing unless you package the web app into some kind of native wrapper.
All of that being said, there are cases where a web app will do fine and can target more than one platform. e-Commerce is a good example. Web storefronts created with an MVC design pattern can swap out a simpler presentation layer that will look better on a mobile device. Go to target.com as an example.
The elusive search for a nice framework that goes past basic HTML and leverages more advanced features across all smartphones has been going on a while. I've seen many, but they either suck completely or will not be accepted into the app store. With iSkygaze, I used a library called IUI to make a web app that seems more like a native app. Today though, there is a new solution and I'm liking it a lot....
http://www.sencha.com/products/touch/
Senchatouch is made by the same people who made ExtJS. It combines HTML5, CSS3 and Javascript to make a pretty nice apps for the iPhone, iPad, and Android devices. Is it a replacement for native apps? No, but it could be a great solution for people developing apps for internal use in a corporate environment where app store visibility is not important.
