I dont see why it would be hard to change the screen resolution on the fly, kinda like what desktop games do. Other apps can use fluid layouts to fit multiple resolutions.

When it comes to other features of the phone, e.g. camera or accelerometer, like one of the posters said- you'll have to do progressive enhancement. Intelligent web developers already know how to do this. You feature test, then you enable a particular feature. Its not all that difficult.