Omer van Kloeten speculates that the reason no one's asked me about C# on the JVM as part of the Sun-Microsoft agreement is because the JVM is explicitly the "Java" VM and .NET explicitly decoupled language and VM. Let's see: according to Jason Bock there are 32 compilers available for .NET. According to Robert Tolksdorf there are 181 compilers for Java (and I didn't count preprocessors).

Obviously, Java's been around for a longer time. Obviously, these are both incomplete pages that have experimental, unfinished, and moribund projects. We can talk about platform strategies and how things might be in the future, but as things stand today the JVM is a more diverse platform than .NET