You don't need to use Java for Android or for the JVM, you can just use Scala. See Scaloid [1] for setting up Scala for Android and Scala Async [2] to get that nice "async" syntax you've mentioned.
One PITA for me is that whenever talks about various technologies happen on HN, I tend to comment on disadvantages, because it's the disadvantages that dictate the best use cases for that particular technology.
But whenever I do that for .NET / C#, there's like a circle of jerks on HN that down-vote everything that sounds bad about .NET.
That's fine, I had some hopes for Microsoft's .NET, now that it is finally being open-sourced and made multi platform, but when choosing a language, you're also choosing the ecosystem around it and this instance, amongst other interactions I've had, confirms that .NET is not for me and probably never will be.
Cheers,
This just isn't a JVM vs .NET competition. If Prolog were the best answer, you could port it to JVM or .NET to your heart's content.
For me Scala is more accessible and elegant than both C# and F# and in my opinion has less baggage.