What I find puzzling about these reports is that no condition worthy of an emergency evacuation of the aircraft has been cited. The emergency (slide) evacuation of an aircraft almost always involves injuries to a varying degree and is not ordered unless the cause of the emergency landing is still developing/worsening. The only thing I can think of that would warrant an emergency evacuation of a safely landed and stopped aircraft would be the threat of fire. The responding airport fire commander is key to assessing the situation regarding the exterior of the aircraft and conveying his/her observations to the aircraft's captain for the captain's decision on whether or not to evacuate.
By the way, the United DC-8 crash in Oregon that you mentioned occurred in December of 1978. That was UAL 173 that ran out of fuel after stooging around the Portland area for more than an hour, while the flight crew attempted to diagnose a problem with the landing gear. The captain became fixated on the landing gear problem and ignored or discounted numerous remarks from his First Officer and Flight Engineer (remember flight engineers?) concerning their deteriorating fuel state. Of 189 souls on board, it was miraculous that "only" 10 died during a nighttime deadstick landing in a built up suburban area (the plane narrowly missed a multi-story apartment building as I recall). This was one of the many accidents that lead to the development of Cockpit Resource Management (now called Crew Resource Management) programs. The irony of this accident was that, while not showing "three green", the gear was actually down and locked.
Cheers,
Grog