As someone who just recently came back to the hobby (and D&D) after 20+ years, I have to wonder how many current D&D players (regardless of edition) even know, let alone understand, these concepts of GSL, OGL, 3PP and so on. It took me weeks to "get up to date" on the debate, time I feel was totally wasted in hindsight. 4E arguably has brought a number of totally new people into the game, has brought a number of former players such as myself back to the game, and I would think a number of people who played a previous edition have "upgraded" to 4E without ever knowing any of this extraneous industry stuff.
In other words, there must be a pretty healthy percentage of D&D players who do not use the Internet as a large part of their hobby, don't use the WOTC boards (or ENWorld, or RPG.net, or any other place where this debate is going on), and may not even know the difference between a WOTC supplement and a 3PP supplement when the time comes. I know nobody has said that the opinions here are the end-all be-all of the D&D marketplace, but I really wonder how much this is all just a debate between a few hundred people on all of these boards, with little or no impact either way on the market?
FWIW, I voted I like D&D and WOTC and do not care about the GSL. I certainly see and understand the potential value to players and publishers alike in having 3PP products, and I empathize with players and publishers who feel they're being damaged by this. But, I simply can't imagine that there's enough real volume at stake to effect WOTC or, specifically, the success/failure of 4E. There are plenty of games out there (yes, with a much smaller marketshare) that have zero 3PP product support, and I don't think the lack of it is what has kept them from rivaling TSR or WOTC. At the end of the day, what they have still doesn't have the name Dungeons & Dragons on it.