HTML/CSS/JS don't solve the problem at all. As they are used today, they target a small set of viewers which happen to go out of their way to provide a fundamen

HTML/CSS/JS don't solve the problem at all. As they are used today, they target a small set of viewers which happen to go out of their way to provide a fundamentally similar presentation on different platforms. If the viewer happens to deviate from how the most commonly used viewers render, they tend to break horribly (see, for instance, a heavy javascript site viewed via lynx). It's easy to do "write once, view on most viewers" when most viewers try to act more-or-less the same and freely break underlying OS conventions because users have learned to expect that web sites will look and behave the same regardless of the underlying OS conventions. On the other hand, when you're natively targeting several platforms with radically different UI conventions outside of the browser, it's a lot harder to provide a single language and library set that can cover up those differences. You could go for the browser strategy and attempt to convince users that your application is exempt from the underlying OS conventions because it's special, but that's a steep uphill climb (especially with users bases known to be hostile to applications which deviate from expected conventions, like the Apple community; god help you if you're trying to sell an Adobe Air app on OS X). Like I said, there is no silver bullet here. You can't get polished interfaces on multi-platforms if you're not willing to polish your interface separately for each platform.