Apple's 16GB iPhone 6S is a serious strategic mistake
vox.com
vox.com
That's not the strongest logic. If the 64GB one has higher margins, adding a 16GB option gives buyers the opportunity to go for a lower margin product.
I think the reason the 16 GB version exists is to give money-constrained buyers an option to buy an iPhone without giving less money-constrained, but money-conscious, buyers a reason to also go for the cheaper model.
This could be same thing in reverse. By having a low-end that is so low, it sets the expectation floor so low that the others seem like reasonable upgrades even though they are actually low/mid-range implementations at mid/high-end prices.