I think you have spoken the point very well. Too add to it, I would point to Apple's refusal to allow users to legitimately re-install iOS 3.
Speculation on my part, but in pondering the reason for this on theory is that they promised iAd investors a presence on an amount of devices that requires an install base that cannot be achieved by the most recent hardware alone.
Pushing users to install a new iOS that is claimed to improve the device, only to have it significantly reduce its functionality, then simultaneously denying users the right to re-install the previous iOS, is hard for me not to see as intentional and purposeful.
My 2nd Gen iPod Touch at $399.99 was the best iPod Touch money could buy less than a year ago. Now there's a forum full of billionaires saying "boohoo buy a new one, whiner!"
Honestly, while I do think Apple should allow for people to downgrade I think your theory is a little far fetched. Or rather I adhere to the simplest theory is the best theory.
And that theory is that Apple has never allowed people to downgrade (at least they don't make it easy to figure out how, you have to be able to find hte downgrade or have it saved from before and know how to trick it to install another OS without itunes doing it automatically). *AND* that this time it was an oversight and the new OS proved to be sucky on the old iphone and therefore there are people who want to go back. Either Apple does not care (likely as I bet this isn't the first time they've had people who want to go back to the old OS) or they didn't realize how bad it was going to be on the 3G this time (I mean there are reports of it running well as well as the reports of it running crappily).