It looks like Apple has added some goodies for us in iOS 4.2:
http://www.mobilexweb.com/blog/safari-ios-accelerometer-websockets-html5
These include:
- Accelerometer support through the DeviceOrientation API
- WebSockets API from HTML5
- Updated HTML5 Form Support
- Partial XHR-2 Support
- Print Support
- New JavaScript data types
- New DOM events
- Enhanced SVG and Canvas support
Full docs have not been posted, but these features should be usable on any iOS 4.2 device.