Not every app has to be beautiful and super-usable though (most business/productivity apps).

If an app can achieve 80% of the usability cross-platform without doing much tweak, I'd say that's a good investment from the publisher perspective.

I agree with you, but for native development, I think I'd rather use a native language---something compiled like Go or D. I do love C# and Python for my own home projects, but for apps that I distribute to others, I don't want to have to ship half of my computer with my app. I'd like to separate logic from UI, write the shared logic, add a platform-specific UI (calling native OS APIs), add a few platform-specific features (provided by the native OS) so no platform-exclusive competitor has any advantage over me, compile and statically-link (only what I need, not a massive runtime) and ship. Like language localization, this process would be repeated for each attractive platform---small, fast, fully native on each platform but with most of the code shared across platforms.

You can do this today with C, but I'd sure rather work in something more modern but which didn't require dragging around half an OS worth of runtime infrastructure. Something more like Go or D, I imagine, if they ever get any traction as client ("desktop") languages.

Well, if you really want to have a native looking experience (even though it seems like apps look more and more different from one another, and increasingly less consistent), you can do that in Java, too, and with probably less work, and for free with world-class tools. I run NetBeans on my mac and it looks and behaves quite natively. Far from mediocre, I'd say.