Most likely you never tried to do what you preach. You will end writing your app only a little bit faster (if you are lucky) and then three times more on debugging.
I have. I built an HTML5 hybrid mobile app for Android and iOS. It was about 90% JS/HTML/CSS and 10% native code. Worked very well for our purposes. You can judge for yourself, it's called Kona and in both major app stores.
Eh yeah. Exactly what I said then reading the Android reviews then? Works on some devices, terrible on most; getting that JS/HTML/CSS to work well on 'most Android devices' is infinitely more difficult than doing it native. Is that worth it? I still want to bet I could've written both apps native in a shorter time with much better results. You can take me up on that any time.
this was going to be my comment on the original comment: it's not like you have to do only HTML5 or only native, or so i'm given to understand... i'd be interested to hear more about the hybrid approach if anyone has links/blog posts.
10/90 is Phonegap/Cordova; when hybrid is viable (imho) is when you need to show complex documents; what HTML was made for. So the parts in your native app where you need to show documents with nice flowing text, images, charts, etc HTML is a good option, but then the 10/90 is usually not native/html, but the other way around.