If it was an uncontained engine failure, then it is luck, not aircraft design that makes an event either an incident or accident. It matters not, whether the control surfaces are hydraulically or mechanically actuated. If a piece of engine decides to pass through a hydraulic pipe(pipes) or cut a control cable(cables), the result is the same, reduced or no control. Put that at or around V1, Vr or climb, then it is down if the pilot flying to use every ounce of their training and experience to attempt to recover the situation.
Passenger aircraft are not designed to contain within its systems and controls, an uncontained engine failure. Thought and design goes into system redundancy, but you do not fire bits of hot engines at airframes and see what happens if?! You cannot predict which bit of engine will not be contained and where it is going to travel after it has left the engine casing and cowl. That is why engines are designed and tested to contain engine failures.
Now, why did it fail? I do not have authorisation on the MD82, but jets are jets. They all use the laws of physics to work. I am making an assumption, so please feel free to flame me, but from what I gather from previous media statements is that their was a problem with a sensor that is used by various systems including thrust management, to derive a temperature. If this temperature was inaccurate, or missing, then it is possible that incorrect thrust settings could have been used or manually calculated, with a possible outcome of an over boosted engine. There would obviously be other parameters to watch such as engine temperature or N speed, but this could be just another hole in the cheese. The engine could have been on watch, with degradation being "on condition" monitored by repeat boriscope inspections, which would normally be OK within its normal operating margins, but on this day, it failed at precisely the wrong time.
Lessons will be learned and god bless the people who have lost through this terrible event.