This is really a question for California Jim, but I'll take a brief stab at it: Either is possible; neither supersedes the other. I myself prefer, for the reason you gave, the simple past. The event has occurred in any case, but recently, so the writer may wish to stress its nearness to and association with the present situation (people fired, turmoil and stress)-- hence, present perfect was chosen (just as I did at the beginning of this sentence).
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