(Trauma increases memory retention.)
Absolutely correct, but the original poster's point still stands. The back of the late, great neuroscientist Gerald Edelman's book "Bright Air, Brilliant Fire" had a quote to the effect that the functioning of the human brain more closely resembles a rainforest ecosystem than the workings of a modern digital computer. Here is the story that I have always used to explain Edelman's theory of Neural Darwinism vis-a-vis human memory.
Imagine that you were in a car accident. A friend picked you up in his brand new shiny red Toyota pickup truck. As you go down the road, you are struck by the cloying new-car smell and the annoying new country music that he has dialed in on the radio. It was sunny as you embarked, but a light drizzle of rain happens as you begin your climb into the mountains on a shoulderless two-lane road. As your friend begins an ill-advised lane passing on a blind curve to pass a slow green Kharmann Ghia, an oncoming white Isuzu utility vehicle hits you and your friend is killed instantly. Certainly traumatic, and your adrenalized system takes a deep imprint.
Now how you remember this is dependant on what triggers each rememberance. Let's fork this out, Choose-Your-Own-Adventure style. Let's say that shortly after this event you buy a new car, a blue Mercedes sedan. You're not consciously aware of why your panic attacks keep cropping up, but it turns out that the new car smell is the trigger. You will remember the new car smell of your friend's pickup more potently, and will be more inclined to emphasize that part of the event when recounting the story. Eventually you might forget that her (see what I did there?) car was a pickup, or that it was painted red.
Let's choose another scenario. Let's say that during your therapy sessions it was constantly raining. As time goes on, those neuronal groups (networks of neurons) are reinforced and you begin to remember that event as the stereotypical "dark and stormy night." That feature will gain prominence in your memories and recountings. We can just as easily imagine scenarios in which a bunch of trips to shitty dive-bars results in you starting to have panic-attacks anytime someone has the poor taste to select "Achy Breaky Heart" on the jukebox. It is not at all implausible that you could eventually "remember" that you were in fact inside the green Karmann Ghia (vaguley), but that you were *definitely* hit by the white Isuzu truck. One way or the other, the emotional impact and intensity of the event will never be forgotten.
So, you're right: trauma increases memory retention. But we are all, as Neitzsche had it, better artists than we realize. (Or, if you prefer, the Zen koan: Who is the master that paints the grass green?) There is no place in memory that is a perfect, digital, untouched replica of an event. A memory is much more like a JPEG with lossy compression: it gets retouched every time it is revisited, with echoes of the particular context in which it was invoked.