ROC Controller voiced concern regarding the turn instruction wording on the Xerox1 SID; claiming aircraft frequently fail to turn as published.

Narrative

A B717 departed in the middle of the first departure push of the morning. I believe that all the aircraft prior to his departure and subsequent to it were issued the Xerox1 SID by the Tower Controller. On the Runway 4 portion of the Xerox1 SID; turbojet aircraft are expected to fly runway heading to 1;200 MSL then execute a left turn to heading 360; while climbing to 10;000 MSL. The previous departure had done this and was turning back to the right to his on course heading; the B717 never executed the left turn and was pointed at the previous departure; although at least 2;000 FT below and more than 3 miles apart. Recommendation; there have been many instances of aircraft screwing up this specific left turn procedure in the Xerox1 SID; many are documented. The wording in the SID needs to be improved so that these pilots do not cut off a preceding departure. In this case the B717 climbed out more slowly than some other air carriers; but another carrier with a lighter load or less restriction on fuel saving might end up closer than we want.