2000 Ford Taurus Replacing coils

Engine Performance problem
2000 Ford Taurus 6 cyl Automatic 110000 miles

We have replaced 3 coils in the last couple of months, and today the car started sputtering like it did each time before. The mechanic syas that there isn't one thing that causes these to go out, and that since it is older it's not uncommon to have to replace a couple of these. Does this sound right that we would have to be replacing so many of these one after another? So far we have replaced te #1, #2  coils.