There is a point there. You're over-playing it, but...there's no total certainty in this area of witness analysis, and it's all psychology, with poorly recorded and re-arranged memories possible, as well as deception. And as soon as it's considered, could become double-deception, triple, a revolving door. Hypothetically.
That could mean eyewitnesses should be totally ignored. Clearly, our media isn't doing that, it's citing them like video cameras that can neither goof up nor lie. It could the lose-lose inversion of what you say I'm taking it as - and that's what the media is doing. By this, if they agree, it's because they both saw the same thing, if they disagree, it's natural variation proving they're real. If they miraculously survived, that happens. If they didn't, we should trust what lines the others attribute to them before the murder they probably personally witnessed from a convenient hiding spot.
Here's what I've found: the more specific you get, the answers to these ambiguities do narrow and can be assessed as more or less likely to be realistic variations as opposed to signs of poor co-ordination. What kind of miracle escape? Why almost exactly one from each and every house? What kind of inconsisties? The color of a person's shirt? The order of their attack? The time of day? Whether they looked and acted like Alawite militias or like Haytham al-Halaq'slocal crew and a bunch of foreigners? Whether heavy artillery or light mortars and RPGs were used? Which families were targeted and tallied? Their religion and political affiliation?
As I said, small inconsistencies will not play in very much, if at all, here. But the big picture is two big pictures. CE is right that no realistic memory difference can explain the vastly different versions told, broadly, by the two different sets of witnesses. One of them must be lying and, apparently, co-ordinating thei lies to approximate reality. Did Assad's people decide to do this slaughter right before Kofi Annan's visit and rely on their known media savvy and a few coached witnesses to get them out of trouble?
Or did the other side, with the actual known record of getting outsiders to believe them, kill and fake their way into it getting pinned on the other side? Because one of those two is probably the case.