John Gruber compares iPhone and Apple Watch introductions in Episode 14 of Electric Shadow podcast (starting at around 1h 24m mark):
I think that the best was the 2007 Macworld expo keynote introducing the iPhone. Let’s see where they go with the watch, but I think even in the most optimistic scenario the watch doesn’t change everything the way the iPhone did.
The iPhone was pulled out of thin air. I think to this day — now we are 7,5 years after that — it was absolutely five years ahead of its time, maybe more. I think maybe if Apple had never released it, the phones we would have been using in 2012, five years later still wouldn’t have been like that. It was impossible. It really is just what it seemed like.
I don’t think they needed a good event, I think they could have had a shitty event to announce it, and if they released the exact same phone seven months later, it would have been fine. It would eventually, with the years, work out.
The advantage of having a perfect event to announce it though was that for the people who opened their minds and just paid attention to it, it gave us a head start as to just what it was that we’ve seen. Half of the people who were paying attention came out that event understanding: Wow. This is amazing. The entire tech world has just changed. And then the other half were, like, this is ridiculous, the thing doesn’t even have a keyboard, no one’s gonna buy it. But if you paid attention, the fact that the event was so perfect, it gave you the context to understand something without ever actually even getting to use the device.