Lots of folks upgrade phones every year or every other year.
To an extent, Apple is producing the Watch to offset the slowing growth of smartphone sales, which tells me that people aren't buying them as often as you think.
I have enough anecdotal evidence of people still using old iPhones all the way back to the terrible 3G :)
What we do know is that about 80% of iOS users are on iOS 8 (=iPhone 4S or newer), as per Apple's statistics or this website:
https://mixpanel.com/trends/#report/ios_8/
And models older than the iPhone 4 seem to very rare:
https://mixpanel.com/trends/#report/iphone_models
So I guess most people update their phones at least once every four years.
If that number is accurate (percentage of users on latest iOS), it seems to have fallen quite a bit, compared to earlier years.
You might be on to something that people are not upgrading as much anymore, since things usually are "good enough" at this point.
If so I'm guessing iOS will then too have to deal with "fragmentation" like it so vehemently has accused Android of being. Interesting times ahead.
My social circle sounds similar to yours. I have two phone junkie friends who seem to be moving to a new phone every year. Then a handful of geek friends who upgrade their phones at the end of their contracts, which is normally two or three version numbers higher.
That leaves the majority who upgrade when their phones break. These range from clumsy people who seem to end up keeping up with my phone junkie friends to some people still using iPhone 3's. But basically... the breakage upgrade cycle sees the majority of them upgrading every other year.
As for anything really keeping me from upgrading, other than a slight fear that the new phone might not be as good as the current phone, I'm really not afraid of losing contacts or anything else. I think I've gotten to the point where the new models aren't really offering a compelling reason to upgrade (other than planned obsolescence as apps get more bloated and OS versions become unsupported).
As for the Apple Watch (and competitors), I think there are three primary demographics: 1. Boomers who look at it as the "Dick Tracy" accessory. 2. Those who like to wear a large, expensive watch primarily as a showpiece (especially since so many people stopped wearing watches when they started using their phones as a timepiece). 3. Those interested in the tech.
I have nothing against the apple watch per se other than price. Just a personal thing. But I can't see paying that much for a device with a) a rechargeable battery that may or may not be easily replaceable and b) has tech that will age out quickly (compared to for example just a digital watch of some sort). Just seems like extreme planned obsolescence. But I'll be happy to be proven wrong.
It may be the utility of such devices outstrips any such concerns.
And every watch I've ever owned has a battery that's just as replaceable as the Watch's -- that is, you take it to the dealer.
Not quite so sure I'd be as happy taking to a ~2 year old $400+ iWatch with a Dremel...
Nor can I, but I'm a Luddite with a cheap Timex and the smallest, dumbest off-contract phone I could find. Given that the $350 low-end model and the $17,000 high-end model have the same battery and guts, I expect/hope that Apple will offer some kind of trade-in or hardware update program. If I could pay $200 every couple of years to replace the non-jewelry bits of this thing, it would make a lot more sense.