I know a lot of people who intend to take that route but few actually get around to it. Like filing photos into albums in the olden days, "sort, tag, and cull" is perpetually on the to-do list, so photos just pile up instead.
However, the regular people I know (i.e. people who aren't photography enthusiasts) shoot far less than the terabyte/year he mentions, by orders of magnitude. For one, regular people don't shoot RAW, and a typical consumer-level digital camera, shooting JPG, produces photos around 3-4MB each. Even if you shoot 2000-3000 photos a year, you're talking on the order of 10 gigs, not 1000 gigs.
iPhone photos aren't the storage problem. Heck, I have lots of RAW photos and my total photo storage is still "only" about 1TB. And, yeah, were I to spend a couple of days culling I could get rid of a few hundred GB of stored pics but that's the sort of boring housekeeping task that never pops to the top of the stack.
However, the regular people I know (i.e. people who aren't photography enthusiasts) shoot far less than the terabyte/year he mentions, by orders of magnitude. For one, regular people don't shoot RAW, and a typical consumer-level digital camera, shooting JPG, produces photos around 3-4MB each. Even if you shoot 2000-3000 photos a year, you're talking on the order of 10 gigs, not 1000 gigs.