In my opinion, the GSL turned out just fine, and Clark got the bulk of what he wanted from the changes.
The sense I got was that one of his partners apparently wasn't enthusiastic about supporting 4e, and Clark was already a bit burnt out by the delay caused by the GSL negotiation, and therefore neither was all that thrilled to go ahead with the 4e projects, and those made up the bulk of the reasons for him to not go ahead with 4e projects.
Clark called out a clause in the GSL that said WOTC could change the GSL on their own, and seemed to make that the focus of his public reasons for not going ahead with the 4e projects.
I suspect that may have played a role, but a smaller role that he seemed to emphasize in his reasoning. Here is why I think that:
1) Most licenses that involve no money coming from the licensee have such clauses. The OGL didn't, but that was an exception rather than the rule. In the "real world", licenses where the licesee pays nothing usually have that clause, and Clark's probably drafted and/or approved of such clauses for his clients;
2) the clause is almost never used and is just an emergency safety measure in case of very rare unexpected consequences of a "Oh My God they published Child Porn with our name on it" nature. In my experience, it's not used to mess with licensees, and there is little to no incentive to do so;
3) even if WOTC ever did change the GSL, it would likely be done in a manner which would have little to no impact on Necro's publishing plans. In addition, there is even plenty of defense to argue that anything already published would be covered by the old GSL anyway;
4) given what Clark knows about how much attention WOTC is paying to the GSL, he probably knows nobody is even thinking about the possibility of changing it, and probably nobody is even assigned the task anymore of thinking about those sorts of things. The GSL is just totally off their radar;
5) Had Necro gone ahead with their 4e plans after the GSL was changed due to Clark's influence, almost all the money they would have made on those titles they would have already made in that year and a half (?), and during that time WOTC never used the clause.
So, I think either the real reasons are more the non-GSL related ones than the GSL issue. Maybe the GSL issue played a small role in his decision, but I bet the bulk of the reason is not related to the GSL, but other matters.