C'mon, remember ten years ago when people said all they wanted from a phone was the ability to make calls?
Actually, no. I remember people saying that the iPhone was too simple - that it only had half the functionality of a Symbian phone and even less connectivity.
Smartphones were seen as a big deal long before the iPhone. Remember "crackberry"? The concept was accepted. Skeptics doubted the worth of the iPhone specifically, because it was quite a bit different from other smartphones (e.g. no hardware keyboard).
Tablets were a bit different, as there were no popular tablets before the iPad. However, the general feeling as I recall it was that tablets as a concept were cool and useful, and it's just that nobody had managed to do one well.
The iPod fit this as well. MP3 players were fairly popular and the advantages were obvious. iPod doubters were skeptical of the iPod specifically, not the general concept of portable digital music players.
The Apple Watch seems to be the opposite scenario. People are mostly not convinced that smartwatches in general are a useful product category, but a substantial number of people think Apple's version of it is good.
It's a departure for Apple. They typically wait for a market to mature to where it's at least somewhat proven, but the existing products are bad in various ways. Then they show everyone how it's done. In contrast, the smart watch market basically doesn't exist yet. There are a handful of extremely niche, experimental products, and that's it. Apple will have to convince people that they want a smartwatch, rather than merely convincing people that they have the best one, or that they've overcome the deficiencies of the other ones.
It will be interesting to see if they pull it off.