Yeah, for awhile each new iPhone was an incredible update; it felt like the flurry of computer upgrades I experienced in the late 90s/early 2000s (which is why Weird Al mentioned "upgrading twice a day" - it wasn't that fast but definitely remember upgrading once a month; build new computer, use it, sell it off and build another new one that would be noticeably better).

I suspect many people upgrade phones now just because the battery is getting old and the cost of replacing the phone is a significant portion of the "free" one they can get by turning it in to their carrier.