I don't think choosing a faster language is premature optimization. Java might be a bit more difficult to program in, but the performance is a lot better. Java is also easier to program in than c++. I think that is a good trade off. I'm not saying you should not use ruby, but not even considering something else seems stupid.
A lot of developers still develop software for Windows and telling them to install some UNIX variant instead of choosing a programming language just seems stupid. Not all of us are developing web applications. But even if we are there are lots of programming languages that work properly in both Windows and UNIX environments that offer the same advantages as ruby, Python or Groovy for example.