I wrote this HN mobile client in less than 3 weekends. it works on Android, iOS and wp8. Also works on all desktop browsers. It took less than 2 weekends, but new chrome on android is a big pain in the ass. Had to rewrite part of it to make it work on latest android chrome.
Also, available on android app store. https://play.google.com/store/apps/details?id=com.premii.hn
It's not easy, but I think you can write very good mobile web app using HTML5 that works on all major platforms.
Just don't use any frameworks/libraries. They are quite slow on mobile devices.