The main differentiators between the models are size, colour and storage. People make a choice. With lots of people not buying their first smartphone, having already had one, they will have had some experience with storage size and usage, no?
exactly.
about 75% of iPhone 6s buyers will be upgrading from a smartphone. That means they know about storage limitations. This isn't like 2007-2010 when so many people were buying their first smartphone and had no idea how much GB they needed.