I just got back from a conversation with my FLGS owner about 4E, and I thought they had a interesting point about sales and the GSL.
It started when I asked them about sales of 4E, and they told me that core book sales had been good, but all of the supplements were moving only in modest levels. I asked if the 4E sales had been comparable to 3E and they said heavens no!
From a FLGS perspective, 4E sales have been terrible in comparison to 3E because they look at the whole line, including third party support, not simply that of products from WotC. The D20 license and OGL brought with it well over 100 books by this time in the line in the 3E and 3.5 days. Think about that in FLGS terms: you're selling maybe a dozen titles for 4E when you had dozens and dozens of books earlier.
As I thought about it, I think that's a key reason people say 4E hasn't sold as well as 3E: because of the lack of third party support. For better or for worse, I had spent a lot more on 3X by this point than I have for 4E.
Does that affect WotC in a negative way? I don't know. My FLGS owner thought that it did because the D20/OGL movement created a buzz of interest for all D&D products that just doesn't exist in our area now.
Just annecdotes, but something to think about (hopefully).
--Steve