Given the levels of NDA, nothing is being said which shouldn't be said; that's not a "conspiracy theory", that's the way things operate in the corporate world. If a game session was frustrating, boring, broken, or otherwise unfun, you won't see a developer posting about it. This isn't to imply 4e is dull, broken, etc -- but any game, no matter how well done, will have off-sessions. Even in the best campaigns I've ever been in, using my favorite systems, there's been some sessions where I've thought, "Damn, y'know, I could have been having unanesthatized eye surgery right about now. That would have been more fun."
I doubt that testers/devs have to submit their blogs for pre-approval, but I'd find it VERY hard to believe they don't have pretty strict guidelines as to what they say. Further, they are all committed, for obvious reasons, to making 4e sound like the best thing since 3e (and I do not fault them for this), so they won't write:"Last night's game was, y'know, meh. Nothing much fun happened. It didn't suck, I guess."
They also assume, more or less rightly, that the Great Unwashed don't care about the mundane details of the PCs social lives or the slow unfolding of complex plots and player debates over issues of ethics (this occupies, oh, about 50% of my game time, both as a player and a DM..."What do we do?" is a major theme, and it's usually a lot of in-character arguing preceeding any action of consequence -- fun to play, not so much to read), so the focus is on the combats, and especially on the (forbidden word) combats.
Saying "The devs want to present their baby in the best possible light" isn't conspiracy theory -- it's common sense.