This. Apple clearly did the research required and it seems to me that a lot of commentators here and elsewhere either simply don't know the size of their current watch(es) or have a strong preference for the still available small, thin cases. Each to their own.
I've not seen an Apple Watch in the flesh yet, but almost all my watches are the same size or bigger than the 42mm
length of the Apple watch and several are as deep or deeper than the 9.5mm
height.
For a long, long time the trend, especially in "sports" chronographs, has been for larger cases and even "dress" watches are generally much larger now than they were back in the 60s.
If you look at some of the top-end brands such as Hublot (oh, how I wish I could afford one of those!) or Breitling then you'll see that 42mm is about the norm and some are much larger.
Bizarrely, some of the more, shall we say, "esoteric" brands make a "feature" of being about the size of a saucer and the height of a small car