Yup, as the Lightning Design System is a Pure CSS framework, we have to write our own javascript for the components.
I have written the code to handle any type of Lightning Design Tabs(default & scoped) in my blog here: http://www.minerva18.com/blog/creating-switchable-lightning-design-tabs-in-salesforce/
And It looks like this:
http://www.minerva18.com/Images/gifs/SLDSTabsDemo.gif
(source: minerva18.com)
I hope it helps, Thanks :D