With the opening up and support of API's on mobile devices, HTML5 has the potential to eliminate the need for device specific development.
The w3c has specifications outlining best practices for Mobile Content and Mobile Web Applications
Features like Canvas, SVG, indexedDB and access to Accelerometers, Gyroscope and Cameras will eventually allow web developers to build a HTML5 site that functions like a native App on iPhone, iPad or Android.
The mobile user just needs to visit the site in a browser, bookmark the page and an icon will be added to the desktop, with all necessary data downloaded and stored locally so that it can work again offline. The Apps can be designed to sync with online data sources.
Browser makers are starting to include these features now.