The instructions for assessing content responsiveness implicitly acknowledges this; what is surprising is the extent to which linguistic quality does influence content responsiveness.
we demonstrated that content responsiveness in DUC 2006 and 2007 correlated with the linguistic quality questions of grammar (Q1) and focus (Q4), and that systems were significantly penalized in content responsiveness when their summary ended Table 6: Correlation and p-values between content responsiveness and various metrics for each "Test" year of DUC.