Seems like a plausible explanation, but I wonder why elderly people start doing this. On the other hand, in a number of these accidents, not only does the driver step on the accelerator, but they don't realize their mistake and take their foot off. I once witnessed an accident at an intersection. The woman at fault, who was not so elderly, did not take her foot off the accelerator even after her car was stopped by the car she hit. In fact she didn't stop spinning her wheels until a passerby opened her car door and told her to take her foot off the accelerator. Some people just freeze after the first thing goes wrong and this makes the accident worse. I think this accounts for some of the cases in which multiple people are mowed down.
My guess is it helps to lessen pain - the hip and/or leg pain that repetitive motions can bring.
...a passerby opened her car door and told her to take her foot off the accelerator.
Now that there's just crazy! Can't explain that one.