Hi,
"responsive" can't be handled automatically. If you add something extra to layout, you have to consider it's responsiveness.
Your website is responsive right now, it loads the responsive.css to fit the core elements in a mobile screen.
You can compare your website with the LightMart demo:
demo.flexiblewebdesign.com/lightmart/index.php
they look almost identical on mobile layout (except you are not using 100% slide pictures in the slideshow -- which don't look good in mobile view)
regards.