While SproutCore uses Ruby to generate static HTML and JavaScript files, you are not tied to Ruby or Rails in production.
SproutCore runs in the browser, your production system can use whatever backend you want, as long as it sends JSON to the browser.
When I was using an early version of SproutCore to build .Mac Web Gallery last year, the backing system was a WebDAV server that produced JSON when asked. I’m pretty sure that WebObjects is the backend sending JSON to the calendar and address book applications demoed at last week’s WWDC.
The nice thing about the separation of browser logic from the backend is that you can build some static JSON fixtures you can serve from your local web server while you’re developing your application.
ETA: Charles Jolley reminds me that you can consume XML as well as JSON, but JSON remains faster.
