Aside from analogies and beyond the fact that there's little doubt Apple is correct, most of their customers have multiple AC power "bricks," there's the fact that the Apple Watch requires an iPhone. So, a customer should have at least the 5W Apple USB charge "brick." What about the new Family Setup? Again, most households have multiple USB chargers but even if they didn't, a quick search of a few large chain US retailers turned up affordable products price from $10 to $15 (
1,
2,
3) -- you don't need an Apple USB charger, it's the cable that's most important and Apple Watch requires very little power to charge, plus you can use a computer or most other devices with a USB port.
The same can't be said for not including a power "brick" with iPhone. Would most have a problem? Probably not, including myself. However, unlike the Apple Watch, the iPhone can stand alone -- my recollection is Apple removed the computer requirement for set up at least a few years back. Is that enough to prevent Apple from axing the charging block/brick from the iPhone packaging? I don't know, but that's to be
discussed more thoroughly in another thread. I bring it up because the rumor is what ignited the anger on the topic for many.