You'd be better off completely removing this to begin with, as even if you did specify the quotes (which should only be on <q>, not <blockquote>, and it makes no sense to include <blockquote> in that rule anyways), you would have to re-define the quotes for every single language (q:lang(...)).
If this wasn't intentional, you should really pay attention to what your CSS reset does and make sure to explicitly define everything it resets.
This is a bug; thanks for catching it. It will be corrected.
As for the intentionality of that CSS rule: it was intentional -- but some time ago; when quotes were redefined in another part of the CSS.
Blockquotes are included because some browsers quote the content of that element too; don't ask which browsers though, as I honestly don't remember -- but older versions of one browser or another definitely did this.
If this wasn't intentional, you should really pay attention to what your CSS reset does and make sure to explicitly define everything it resets.