WOTC does NOT want 3rd party products with 4e. From the GSL's orginal relase, to its slow division, to wotc's delay in handing out the GSL to 3rd parties.
They dont want other folks in their playground in 4e.
As others have pointed out, there would be a simple way to achieve this - namely, no GSL.
A good license is give and take - the OGL had restriction, but allowed things that would otherwise have been prohibited.
The D20 STL was more restrictive, but allowed (in fact demanded) the use of the D20 logo. Making compatibility obvious.
The problem is that the GSL tries to combine both licenses, then adds more prohibitions on top of it, without many of the benefits of the OGL. You gain the use of the 4e logo, but are severely limited in what you can do under the license.
Well, the GSL is give and take - indeed, it has to be in order to create a valid contract. What is given is the right to use various WotC trademarks, and what is taken away is the right (i) to use text from 4e rulebooks (some, perhaps much, of which would enjoy copyright protection in any event) and to use non-copyrighted game terms (like "elf") to describe something different from what they describe in the 4e rulebooks.
When people talk about the benefits of the OGL, I think what they really mean is not the OGL per se, but the SRD released under the OGL. And from its subsequent behaviour it is pretty clear that WotC believes the benefits of releasing the bulk of its rules text - in which it might otherwise have asserted copyright - under a royalty-free, irrevocable licence flowed mostly to the licensees, rather than to it as licensor.
How is not supporting their 3pps, which help get market penetration with no cost to WotC oppositie to established policy? That's just a silly statement.
It makes good business sense to follow Chris's suggestions. Is it WotC's goal not to use good business sense?
Presumably, WotC is not acting irrationally (by its own lights) in respect of its licensing policy. Therefore, I assume that WotC believe (and presumably on the basis of at least some evidence) that in fact 3PPs do little to help market penetration, or alternatively that the increase in that respect which would be achieved by WotC support would not justify the costs of providing that support.
I think the existence of a license that says "write adventures to support our game but don't you DARE create anything new" vs. the license that allowed Spycraft and M&M is where I decide to call the GSL 180 degrees from the OGL.
It seemed to me, that WOTC didn't *really* want full throated support for 4e from 3PP's. Sure, some extra adventures from us would be nice, but they didn't want any settings including variant rules
I think that your last clause slightly exaggerates the restrictions that the GSL imposes, but in general terms you must be correct - because if WotC had wanted games like Spycraft and M&M they would have offered a different licence with different permissions and different terms.
Applying the same principal that WotC is acting rationally by its lights, I assume that WotC believes (and presumably on the basis of at least some evidence) that it is in their best interests not to release their rules text under a royalty-free licence in a fashion that would permit the creation, out of their rules text, of games like Spycraft and so on.
The OGL+SRD was an experiment. Ryan Dancey had a hypothesis - based on network externalities etc - that this move would offer commercial benefits to WotC. WotC's decision to create a game that in many respects diverges from the SRD released under the OGL, and the rules text of which is not itself released under the OGL, suggests that WotC formed the view that Dancey's hypothesis was disproven.
The GSL can also be seen as an experiment, namely, to see what interest there might be from 3PPs in publishing material to support 4e that would not demonstrate the type of variance and departure from the assumptions of the game, nor the duplication of rules text, that grew up under the OGL+SRD. It seems that the answer is "not much".
This does not necessarily show that WotC is evil or stupid, anymore than it shows that 3PPs are evil or stupid. It may just be that, in fact, there is no model for 3PPs of D&D that serves both WotC's interests (as conceived of by WotC) and 3PP interests (as conceived of by 3PPs).
(And as others have said, Paizo is in a completely different situation from WotC - given that its game depends utterly on the OGL+SRD model it is
going to have 3PPs in orbit about it, and it may therefore be well worth the cost to Paizo of bringing those 3PPs into the tent, where Paizo can have some influence over their direction and output.)