The way I see it, this entire conversation is predicated on the idea that Paizo is now a major competitor with WOTC.
This now seems to be the received wisdom on these boards. I don't have any evidence independent of what I read here, so am just going with the flow.
I do think that 3E was largely "done" and it was time to move on.
My feeling is that the apparent success of PF suggests this may not be so - unless you are counting PF as a "moving on" from 3E - which may be so, but I don't think it's moved very far.
What the success of PF/Paizo
appears to show is that - contra to what Ryan Dancey said back in the day - there
is a viable RPG business model which puts adventures, rather than character build and encounter/world design supplements, at its centre.
I don't know whether or not WotC anticipated this, but suspect that they did not, and thus did not anticipate that Paizo could use its experience at adventure design in combination with its subscription list to keep 3E alive in the way that it has done.
What remains, for me, a great puzzle is WotC's inability to produce strong adventures. I don't want to say it's a
crippling weakness, but it certainly seems to be hurting them.
Paizo was not the first publisher to repackage the core rules and publish them. At least two other publishers did that from 2000-2008 and there were probably others that I'm unaware of. And there were others who tried to publish various flavors of "D&D... but slightly improved!". None of them were successful. None of them significantly impacted WotC's market. None of them enjoyed the success which Pathfinder has enjoyed.
I feel fairly confident in saying that no such project would succeed in yanking away substantial portions of WotC's marketshare, as long as WotC remained at the top of the pyramid. It was only by vacating that position that WotC made Pathfinder possible.
I think what is distinctive about Paizo is precisely it's ability to use adventures (and subscription to them) to leverage a system, rather than vice versa.
The best sense I can make of WotC's decisions and subsequent situation is that (i) they were concerned about a growing challenge from OGL publishing of their rules system, (ii) they did not consider it a viable option to continue to dominate d20/OGL+SRD gaming by publishing adventures and campaign supplements, and therefore (iii) decided to change to a system that would not be so easily replicable via the OGL+SRD, and that would not itself be released under the OGL, and also (iv) appeared to believe that there was a strong market - whether among existing or potential players - for a markedly non-simulationist although in other respects fairly mainstream fantasy RPG.
They have achieved (iii). It seems that (iv) turned out to be false, although my own view is that WotC has not done itself any favours by consistetnly failing to present guidelines, GM advice and adventures that make the most of 4e's strengths. Whether or not they had any inkling that (ii) might be true for them but false for Paizo, it turns out that it was radically false for Paizo.
People will tell you that the mechanical end of this could be released "open" just as easily for 4E now as for anything else. It is the copyright parts that can be protected. So really, it shoudln't make much difference.
As I've posted recently on a couple of other threads, I don't think it's quite that straightforward. First, it's hard to produce RPG material that doesn't combine some fiction with the rules text - and if the game is to be a D&D claim then WotC may well have a copyright claim over the fiction. Second, in order to present the rules text in such a way that its status and utility as a clone is evident, it will be necessary to replicate to some extent at least the structure, headings, etc of WotC's rulebooks - at which point, again, there may be reproduction of not only of rules but of other elements of WotC's works in respect of which it enjoys copyright. (I feel that this only gets trickier when the publisher of the clone want simultaneously to say "Hey, I'm selling D&D over here" without actually making wrongful use of WotC's trademarks.)
Now while I am an academic lawyer who teaches some private law, I am not an IP lawyer, and so the above is presented in a fairly general and tentative fashion. Frylock is a poster on these boards who is a practising IP lawyer, and he has expressed the view that a 3pp character builder is doable. On the other hand, Clark Peterson of Necromancer games - also an experienced commercial lawyer - has expressed the view that OSRIC is "infringing and unethical", and I assume that his reasoning is similar to what I have sketched in the previous paragraph. (I understand that Kenzer has expressed similar views about OSRIC, although I've not actually read these.) OSRIC is of course not the only way to clone, and so what Frylock and Clark have to say isn't necessarily at odds. The point I'm making is that succeeding at the task is probably non-trivial from a legal point of view.