Some vehicles and engines may have been more prone to sludging than others but it still boils down to one thing; change the oil more often or use a synthetic and the problem will not occur.
While the 3000-3500 mile oil change interval is often dismissed it is a necessity in many cases due to the car owner's driving habits and enviromental conditions.
Changing the oil every 5-6k miles on a car that only sees 2 to 5 mile trips is not good enough.
It would be interesting to know the details (oil change intervals, type of oil, type of driving, etc.) behind the comparatively small number of vehicles that suffered any damage due to oil sludging.
I guarantee you this. When someone with a prematurely failed engine due to engine sludge is standing at the dealer service counter there is no way on earth they are ever going to admit to bad driving habits, lack of maintenance, or anything else.
They may only change the oil every 10-15k miles but they are going to look the service writer or service manager square in the eye without blinking and swear to the Vatican that oil was changed every 3000 miles at the latest.
The 3k miles figure usually surfaces after being told that the oil was not changed often enough, go figure.