There's no point in saying this because I'm addressing people who are thinking irrationally, but: there was no logical reason to believe an iMac update was coming today. If you thought there would be a 27" retina display you were seriously dreaming. Obviously these things are coming eventually; every device Apple sells will have a retina display soon enough. Apple wasn't "supposed" to release anything today, you just hoped they would.
Just remember this when you're composing your description of how much you hate Tim Cook and how he's ruining Apple.
I agree that a lot of hatred of Cook - no idea why - has boiled over to ignorant moaning, but "no logical reason to believe..." is more than a little off. Its average cycle for the last five versions has been 273 days. It's now been 405. There have been several leaks and rumors such as
this or
these which are no less viable than the same ones that people cited for guessing, correctly, that the others would be upgraded. And believing that the lack of a retina display being available immediately on one of the current iMac models holding back an update of the line, or even a mention, is pretty far fetched.
The iMac, second only to the MacPro (whose average upgrade cycle is historically twice as long and was updated today), in a calendar sense, was the most due for an upgrade. Historically it's the entry option for non-student new Apple computer consumers. I'm very surprised. Also rational... mostly.
Just remember this when you're composing your description of how much you hate people you consider to be thinking irrationally. <3