CSS Menu Writer And CSS Sculptor wont generate responsive designs by default, but they can be edited after they are created to become responsive.
see this thread From Mike T on editing CSS Menu Writer to become responsive:
http://www.webassist.com/forums/showthread.php?t=29212
You are not tied to using CSS Sculptor layouts in Site Builder, you can design your own responsive layout, save that as a template, then create a Site Sculptor design from the responsive template.