Making HTML5 widgets tha look like iphone widgets is one thing, but making them perform equally well is another matter altogether. Performance of html5 animations (even plain View Transitions), scrolling long lists, responsiveness to gestures feel sticky and jerky. An iPhone user will notice the difference.
There's also some differences in the kinds of gestures that are supported by different devices which results in platform specific code and usability issues as well.
I'll stay with native apps for now I guess.
