You may not be screaming, but you did call it a 'catastrophe' when it hasn't even slipped past the official release target.
I'm sure that the actual final ship day isn't planned terribly far in advance, but the whole product release and production process surely is. For a product that doesn't need to hit a specific announced date (iPhone, iPad), they probably start selling them as soon as they are confident that they have a decent supply without major production issues. They might wait for the next tuesday/wednesday, but that's probably about it.
They aren't going to release the iMacs until they can make enough of them reliably, nor will they keep thousands of them stuck in warehouses just to make people wait. Doing either of those things would hurt them.
I'd say what has happened with the iMac qualifies as a catastrophe - regardless of when Apple said they would release, the fact is that you haven't been able to buy one from Apple (of any vintage) since October, unless you hunted in the refurb section. That is a catastrophic hole in your supply chain leading up to one of the busiest shopping seasons of the year.