That's not really Python or Ruby in the browser, that's IronPython or IronRuby running in the Silverlight's CLR via the plugin. Yes your Silverlight app can get out to the DOM and vice versa, but it's not really what Silverlight was meant for.
If you want to be pedantic and get into a debate nothing is really ruby as the language lacks a spec the best definition of Ruby we have is acts kinda like MRI 1.8.
Also, most browsers don't run really run Javascript, they run ECMAscript or JScript. It's really jQuery converted to bytecode/assembly/C on SpiderMonkey/JagerMonkey/V8/Nitro. Sure you can create a high performance web server, but that's not really what V8 was meant for.
(I don't think I'd do this myself, even though I like Python quite a lot.)