Maggan said:I would be surprised if WotC didn't already pay attention to stuff like this.
I would be extremely surprised if they shared that data, though.
Bingo.
Sholari's questions are, indeed, all *answerable*...but, unlike sales numbers, you need to do a "primary research study" (i.e., conduct surveys) to answer them.
WotC does this kind of research, though they may not ask these exact questions. Typically, to do this kind of research, WotC works with market research suppliers who have large (e.g., hundreds of thousands of households) research panels that can be used for such a study. (You use that kind of panel, rather than relying on the people who send back the comment cards in the book, in order to make sure you have as representative a sample as possible.)
However, the problem is that this kind of research isn't cheap. WotC (and probably Games Workshop) are the only game companies with the kinds of resources to do this kind of thing. And, to really get at Sholari's question (i.e., are these numbers declining), you need to redo the study on a regular basis (probably yearly), in order to see the trends.
And, as Maggan points out, the company that pays for such research isn't likely to then release the results to the industry (a.k.a. the competition). As a rule, good market research is a competitive advantage, and you don't give that up easily.
It's possible that you could see an industry organization (i.e., GAMA) do something like this...but remember that RPGs are a fairly small part of GAMA, and I'm not sure how much of a budget GAMA has, anyway.