If you go the 80/20 route, you'll only need an iOS anyway, and later on you can add an Android app - that's what they all do now, anyways. Perhaps that will shift to Android-first when everybody and his dog has a cheap Android phone (I hope not!).

Pseudo-native HTML apps are inferior, and people will notice it. I'm quite fed up with the FB apps on both iOS and Android because they spend more time with loading than the in-browser version. It's so bad that I actually considered if FB wants to drive people away from mobile so they click more ads in the browser - I don't think that's really the case though.