Well, since they do market research that is unrivaled in the industry, I'd say they probably know their market a little better than we armchair theorists do.
I'm sure they know it better than we do, but y'know, market research has lead so many companies into so many terrible errors, even when "armchair" theorists have be telling them "No, no, no." that I'm not sure what you're saying has much real meaning.
Blizzard with WoW are an example of this. Blizzard do market research virtually unrivalled in the industry (only Bungie under MS did more). Yet they were totally blown away by WoW's success - their market research had indicated it would be a game of middling success, and whilst bringing in a lot of money, would be more likely "comparable" to other games, or a little higher in population. Not the multi-million player juggernaut they found. Luckily they had the money to slam up servers and churn out discs at a rate of knots and expanded with the market (though their CS lagged a year and a half behind because they couldn't recruit fast enough).
Further, even after release, they've been told "This is what you should do" by the public, at length, and very rationally (I'm not just talking one crazy screaming-filled thread on their messageboards, but the more rational arguments and so on), and have ignored it, often openly poo-poo'd it, and then, shock, a few months after that, apparently realized it was right and implemented it. The lack of real competition has given them the breathing room to do so without losing customers, but in a more competative market, it wouldn't have.
Maybe WotC are in the same place. Even if their market research isn't perfect, their market dominance is so assured that they can "error-correct" later based on post-release research, rather than needing to get it perfect "out of the gate".
Regarding the "scaly" debate, I think WotC were actually smart to put a scaly race in core. Those saying there is considerably desire for such a race are spot-on, and I do think it'll help 4E, even with the "far out"-ness. I think the choice of a draconic race was smart, too. I just think the "fatdragon" look they chose, with no tails, horns, neck or wings was, well, a bit lame, and not likely to strongly appeal to the "scaly" fans. It doesn't appeal to me, and I've played a dozen lizardman-types over the years.