Responsive Blocks is called Stacks.
Blocks was designed as a rigid fixed layout system (similar to iWeb) – but that sort of layout has obvious disadvantages when things need to be responsive.
As soon as the iPhone was released this became pretty obvious to me… I started working on Stacks pretty much the day after I bought my original iPhone. Stacks launched about a year later.
We keep Blocks around because it’s still is useful for building certain types of pages and there are a few folks that need exactly that.
But if you’re building a whole site – which on today’s web really really should be responsive – then you should build it in Stacks or other responsive page-styles, with a nice responsive theme.