Yeah, all the feedback they received after realeasing 3E that resulted in 3.5.Nifft said:Perhaps you mean feedback about 3.0e went into 3.5e? That would be true, but wouldn't really be relevant to 4e.
-- N
All that feedback did result in the ultimate version of the 3rd edition D&D, 3.5, so maybe the same kind of feedback could antecipate the definitive version of the 4th edition D&D.
They already said there won't be any 4.5 and I believe them, but I don't believe things won't need changes in the coming years after they released 4E, so maybe they could antecipate most of these changes opening the playtesting now for everyone.
But they know what they're doing so if they didn't do it, maybe it's not that easy and useful as it looks like. Playtesting things that are done is different from playtesting things that are on the flux. I dunno.