My guess is that something has gone a bit tits up at their end...
Maybe they found some bug, maybe a security glitch, or something isn't quite right. The hint above that they are "working with Intel" (and assuming they are telling the truth here) would suggest that the ICS build wasn't as complete as we thought it was.
I was watching a video Google did for developers a couple of days ago. There was a guy on there who does certification for carriers. It seemed an unbelievably stupidly complex process. All sorts of test suites, regressions tests etc. etc. etc. His job was not my idea of fun.
My guess with us is that the upgrade path isn't too clean. I've lost count of the amount of times I've read "Do a factory reset" when installing a new custom ROM for my old devices. Even between releases of the same ROM, that's often the advice. They probably want a way of updating without wiping the device, and they are struggling to make sure that's working properly. But I'm only guessing.
It's all speculation at this point. It would be nice if they were just open and honest about the whole thing. "Sorry guys, we're delayed two weeks as we found a bug in the sound service", or "Yeah, one of our engineers just got hit by a bus"... It's the wall of silence, lies, and marketing crap which I think annoys more than anything else. If we had the honest information, I think many people would be more willing to accept and wait.
I can't see them deliberately delaying the update. There is no benefit to them, and I'm sure they don't want the bad vibes. Writing e-mails isn't going to help anything. Yeah, they've lied about release dates, and yeah, it sucks, but nothing we can do at our end will speed up the process. It'll be released "when it's ready", which is how it should be.
At the end of the day, we still have a device that works, and works well with Gingerbread. There aren't many bugs, and we're not loosing out a great deal by not having ICS. Sure, it'll be better when it arrives, but I'd rather wait and have a stable phone I can count on, than a phone that's buggy as s*** and annoys the hell out of me. I'm sure most of us have had an experience flashing a crap rom which makes things 100 times worse.