So much for that toyota quality..

Electronics can fail, but then mechanical parts can fail also. I sure don't miss the old mechanical voltage regulators with the reed switches! Engineers must consider what would happen if a system fails, and what is the chance of failure. A broken cable in at traditional accelerator is possible, but it will merely cause the engine to idle- potentially dangerous, but not as bad as unchecked acceleration.
The operators of those Toyotas could have put the car in neural, taken the car off the road, and cut the engine. But people panic in these situations and don't do the logical thing. Would anyone actually use the mechanical emergency brake if their hydraulic brakes failed?