The author put down in writing what I have been thinking all along. As a new Java developer, I'm amazed how big the Java open source community is.
I think a lot of it has to do with the fact that the best minds in .NET open source (eg: Miguel de Icaza and the Mono team in general), are too busy reimplementing everything Microsoft has already done. It's a waste of talent really. But there is a demand for cross-platform .NET and that demand WILL be met, if not by Microsoft by the people who run the Mono project. It would be better if Microsoft would open source .NET.