One of the main reasons dampening rollers do not last as long as ink rollers is that on many presses the dampening rollers are subject to vastly more surface friction than the ink rollers are. In the Heidelberg Alcolor system for instance, the pan roller and chrome rollers do not turn at the same surface speed and the speed difference between the chrome roller and form roller is high. If the rollers are set too tightly in these positions, friction will wear the rollers quickly. The various elastomers used to make rollers can be chosen to optimize one property or another; poor dampener roller life is usually due to an elastomer with poor abrasion resistance used to make the roller in order to maximize some other property (chemical resistance, some surface property, etc).
Daniel T Roll