The myth about simple cross-platform development in Java is just that, a myth. Anybody with cross-platform Java experience will attest to this. Java, as a language, has grown stagnant, while C# has continued to evolve.
I and our team of 100+ Java developers will disagree with your statement of Java and cross-platform development. We find it excellent. Is it perfect? Nope, but in my opinion it would be a 9 out of 10 with the next closest competitor being.... Well there isn't really any close competitor but I guess we could give the C language a 2 out of 10. Perhaps Ruby is good but I haven't looked at it. Granted I am talking more about the JVM that Java itself. However, Java like other languages has evolved quite a bit in the last few years.
Does Java have the radical changes that say languages like SCALA have? Nope, but then again it shouldn't have that. Is it stagnant? Not at all.
The core difference you see between any of the Microsoft languages and the JVM languages is that the JVM languages somewhat try to work within the community. They also want to maintain binary (class) backward compatibility. Microsoft is an absolute dictator with their language and even to a large part their tools. This does have it's advantages, in that stuff comes out quicker, but then again, if you are a business and built you lifeblood one VB6 to have it brushed aside by Microsoft, you might be a little angry about that ruthless dictator approach. If you are some contractor type of person who wants constant change in the core framework to make your life easier (at the cost of compatibility), then you would probably like this approach.
So in short things like closures will be in Java 7 (not a small task), and Java the language is not at all stagnant. Cross platform development, testing and support is excellent with Java. We use OSX, Ubuntu, Microsoft Windows XP and 7, and RedHat with no problems.