2) Performance is not all that matters. Getting back to the easier to code argument, productivity is equally as important. If the developers of the product are more proficient in Javascript, then working around the performance issues is likely cheaper than waiting for the developers to learn another language better, or to hire developers who know Java or C or whatever and understand the vision of the product being created.
Not to mention these days performance is cheap. Run several instances of node.js behind some sort of load balancer/proxy on a multi-core server and you're good to go. Heck, my little cheap Rackspace cloud server has 4 cores available to it.
The language and platform is only part of the equation to developing a product. Whatever allows you to create a product you can develop quickly and maintain in the future is the right choice.
Disclaimer: I tried node.js, decided it wasn't for me and went back to Tornado (python). I however can understand why someone more proficient in javascript would choose node.js. It was really easy to set up and get into writing code with.