Ummm... Read my post.
They are the 100 Top Selling Small Press Products. If it can demonstrated that 4E can consistently beat Fate, Icons, Pathfinder, and Savage Worlds in the top 100, you would have a valid argument. Your argument is not valid because there are are ZERO products in the top 100 on DriveThru Small Press list today and from my long term observations this is typically the case. 4E products do not consistently make it to the #1 slot on that list. Pathfinder products do, Icons products do, Fate products do, Savage Worlds products do.
Yes, but so? That's not the point. The point is "Why should WotC care?" if the answer is "Because then I, the 3PP, can sell more stuff" then that's irrelevant to WotC.
The Open Letter is an essay asking WotC to make it easier for 3PPs to sell 4E products. It asks for a list of things. It does not make a case why making it easier for 3PPs to sell stuff is in WotC's interests - it's literally just a begging letter.