The first question is, are they asking the right people.
Well, there are only two types of people who matter: existing D&D customers, and people who would be D&D customers except for some flaw they find with existing D&D products (including finding the game inaccessible).

The play test best addresses the first type of people. After all, if you're a customer, you want to know what's going on. The play test also gets some of the second group (mostly those that played 1e, 2e or 3e and left recently. The rest of the second group is unlikely to be interested in the play test either because they're not RPG players now, of have never been interested in D&D as anything more than idle curiosity.

There is a third subset, which is the group of current customers who aren't actually interested in the play test. These are like some of my current players who are mostly there to hang out and have a good time beating up some orcs. They aren't particularly attached to the game, and don't spend a lot of time thinking about it. They will likely simply play whatever game their DM has chosen for them. These people do have some useful feedback to provide, but short of actually ambushing them directly, most of that feedback will be filtered through their DM who falls into the first group of people anyway.

So I would say overall, yes, they're asking the right people.

The second question is, will the majority answers be successful in drawing in new people and maintaining them?
The answer to this question is no. And it is always no, no matter the questions you ask. New product development is not about asking people what they want and then giving it to them. That's skating to where the puck has been. Development is about asking people what they want, and than giving them a new and better product which addresses the underlying needs expressed through their wants. If you're a computer person, this is why Apple does so well selling things that on paper are measurably "worse" than their competition (iPod anyone?). It's also why Microsoft Office remains the dominant office product despite being universally hated. This comic also covers it a bit: http://media.smashingmagazine.com/wp...models_v61.jpg

The short answer is that you will never get the "right" answers from the questions you ask people when developing a new product.

The nature of their questions is, IMO, wrong. The surveys are all about the fluff and gut feelings, not about the mechanics. It's a lot of, "What's iconic?" and "Does this look like a bugbear to you?"
That's because the mechanics don't matter at this stage. Look at it this way, most people who play RPGs are not mechanics geeks. It doesn't matter to them whether or not their probability curve is generated by 4d6 or 3d8 or even 2d12. What matters to them is how the game feels. How it evokes the world that they're creating. The absolute most important thing to do when designing an RPG is to decide what you want the game to feel like, and then craft your mechanics to support that feel. To that end, it's vitally important to ask "What's iconic" or "What does a bugbear look like to you?" Once you have established what the game is supposed to feel like, you can then tweak and simplify your mechanics over and over until you find the right mechanics to provide the feel you're looking for. That isn't to say 4d6, 3d8 or 2d12 don't generate different feels, but that whether that feel is consistent with the activity that we're trying to model is far more important.

If there's one thing I've learned from playing RPGs is that if I buy a game, I want it to be one I couldn't have made myself.
Then you will never buy another RPG again. The fact of the matter is, any game a team of "professionals" can design, is one that you could have made yourself. It might take you longer, and be more difficult, but there's no magic sauce that makes a professional game designed better able to design games than you or I. Also, never ever ever forget that no only was D&D (and indeed the entire RPG industry) the result of a bunch of "hobbyists", but that almost every single professional was a hobbyist before someone decided to start paying them.

Yet WotC isn't spending their time developing those mechanics or even introducing new ones. Instead, they are sending out surveys and polishing the skeleton instead of adding meat to the bones.
If your foundation isn't solid, the building will never stand.

I've said it before and I'll say it again: WotC is abandoning (at their peril!) their strengths as a game development company and is instead trying to retread the ideas that were popular during their first big hit -- 3.0. Appealing to nostalgia might get you some money in the bank, but it is invariably the death knell of a franchise.
What are these "Strengths" that you see them abandoning?