Regarding the Watch is the idea that Apple held back a key aspect of the product. Not a standard feature, but something major. The kind of thing that would elevate it from mere accessory, to something that one day could replace an iPhone.
But in todays busy world you only get to launch a product once. The fear of bombing is enough to stop anything key being held back. In fact the problem is often just stopping this fear from resulting in an unfocussed presentation which does not zero in on the two or three elements that make the product understandable and desirable.
Do Apple even have a history of holding back major aspects of a product? Sure they don't detail every tiny feature. Yes with iOS beta's they do not reveal aspects that give away details about the soon to come iPhones. But major features that are only announced at shipping?
What about keeping details back so competitors cannot copy them before the product launches? Again this rings hollow. Apple have a whole lot of other issues medium term if the Watch can be cloned in a mere months. Compare that to iPhone and how it lived up to being five years ahead of the competition.
Looking back at the video of the event you can see an Apple that is going out all guns blazing. The event itself was back at the Flint Center, "... on this stage we introduced the iMac. Which signaled the rebirth of Apple. Today, we have some amazing products to share with you. And we think, at the end of the day, that you will agree that this too is a very key day for Apple."
Then Tim Cook announces (55:45) "We have one more thing". It made me wince to hear this classic Steve Jobs line. Was it too personal to Jobs for it to be used again? Not on this day.
Compared to the focused beauty of the iPhone launch, what followed was a laundry list of features making it hard to think back to anything particularly memorable. Overall, far from being a day where anything was held back, it was a day that sorely would have benefited from it.