Lately, observing the iPhones, I have had a feeling that they love to go incremental. Of course it helps the bottom line, making people upgrade by adding 'just enough' but I do think that if they go on a biennial cycle of hardware releases, the customers might be seriously happier.
Case in point: I did not buy the iPhone 7, because I knew they will eventually add True Tone to it. They should have done it, but they held back. Admittedly I do not _know_ if they really could not, but Apple used to bring seriously loaded hardware, but with the iPhones being on a yearly cycle, they have had little incentive, and personally, I do not like the approach.
They gave a DCI-P3 display on the 7 (IIRC) but just not True Tone. To me, their incremental update mindset was really clear with that. On the other hand, the 8 is what the 7 could have been, minus the wireless charging and A11 of course.
With the watch, they were in new territory and while I have not followed the watch very carefully, but all upgrades to the watch have seemed to be really, really good. Series 3 is really loaded at the moment and there is no reason not to buy one now if one needs it now. I do not need it but instead want it, so I am hopeful of curtailing my wallet back until I see the impending design refresh.