Whilst agreeing with the annoyance factor in principal, Danny (trust me controllers find it every bit as annoying having to prompt for mandatory read backs), I believe that a seperate QNH check is a necessity due to possible transcription errors and the importance of correct pressure setting for seperation, terrain and avoiding level busts.
If any of the other information taken from the ATIS was incorrect then the problem would be readily apparent from controller clearances, information or other sources (except perhaps temperature and dew point!) with little impact on the safety operation.
However, with inbound aircraft in particular, an incorrect QNH is likely to go unnotticed until after the event has occured.