There was a long of talk about what he was going to do, but between the GSL replacing the OGL and the actual 4e release...
Clarification:
The GSL did NOT replace the OGL. The OGL is the Open Game License. It's still around, it's still being used.
The GSL replaced the d20 STL. That's the license that was used for everything with a d20 logo. As an aside: Basically anything you see currently being sold with a d20 logo? My understanding is, it's basically illegal (in violation of the d20 STL); WotC revoked the d20 STL and gave a time period (6 months as I recall) for all d20 logo product to be dumped.
At the time this whole debacle with the GSL was going on, there was quite a bit of question as to what was going on with the licensing in the first place. Previously, publishers had the option of using either license. With the advent of the GSL, things got very confused, especially as there was constant chatter about what was going to be happening regarding 4E and the OGL.
The GSL was a further problem, because it wasn't just a "redo" of the old d20 STL, but in fact a much stricter and (I think) somewhat harsher license. Eventually everything sorted itself out with the GSL as we currently have it, no OGL option for 4E, and as an aside there's also no "fan license" version of the GSL either. The ability for WotC to revoke the license and what might happen to IP which was produced under the license was worse (and I think murkier) when the d20 STL was dropped and the GSL adopted in its place.
All of this is kinda important, since it basically means that Necro wouldn't be able to change anything about the 4E system; so basically, the whole "old school feel" was pretty much impossible to do if doing so required _any_ sort of redefinition of _anything_ (something strictly forbidden by the GSL).
Clark had talked a lot about doing something, but I have yet to see anything akin to a critique about what he liked about 4e and what he hated--at least where I looked.
I believe that at the time there was the belief that publishers would have a greater degree of freedom than they were in fact given. That being the case, why bother complaining about an edition that's a done deal, when you can simply alter the bits that annoy you?
Most of his comments are a lot more vague than other publishers. Most publishers made a decision earlier in the game, and even went into details about what they liked or hated about the new ruleset.
A lot of publishers also simply walked away from WotC pretty much at the outset of the GSL coming out. There was no way they'd be able to actually run their business as they were used to and this combined with significant changes to the rules that they were unable to change in any way as a product.
As well, WotC kept folks hanging for a _long_ time when it came to the whole license thing. Folks jumped ship because they wanted/needed to be able to get product written and printed in time for conventions (like GenCon) and WotC dithering about with the license was an unacceptable delay.
And finally, I _think_ that there was negotiation going on behind the scenes in terms of licensing etc. I seem to recall some posts that suggested that and were essentially "talks are ongoing but nothing can really be said publically".
I'm not judging him changing his mind, just that in this whole process he hasn't gone into many details like why he likes PF better than 4e, or (before) vice-versa.
Basically, Clark was a huge supporter of D&D. Like it or not, 4E coming out means _that_ is the new version of D&D and even if folks still dig the older versions of it (which was part of what his company was about afterall), it had still moved on. I always got the impression that he was more of the opinion that rather than pointlessly complaining about something that's a done deal, you should get on with what you want to do using the tools at hand. And at the time, it looked like that would still be possible.
The landscape changed, it no longer became possible, and given the choice of churning out product under the restrictive license or not, he chose not.
One of the biggest things for Clark to like about Pathfinder? He can make the products he wants, the way he wants. He can change things, add things, and redefine things, in order to arrive at exactly the place he wants to. Make a monster tougher, change its abilities, whatever.
I get the impression that as far as you're concerned, it's mainly a matter of what system Clark likes or whatever. And I don't think it really is. The way that certain aspects of the _only_ license possible to use for 4E material could be interpreted appears to be a major concern for him. That being the case and the fact that Pathfinder is the current thing closest to "baseline" 3.x rules that's being published and combined with the system mastery required to produce a quality product.... if he wants to contribute professionally to the hobby of D&D or D&D-like games, he really doesn't have a whole lot of options.
I'm not trying to be a jerk, just trying to offer up what seems to be a perspective you haven't considered.
Disclaimer: I'm not a lawyer, I only own a couple of Necromancer products, and I don't know Clark Peterson. Everything above is based on my own human (and therefore faulty) memory and understanding of things.