If you load a buttload of mp3s on there and / or a small library of movies and tv shows, then 16GB is not that much. Especially once you add in a few hundred photos at 3 or 4MB a pop. And some of the more graphically intense games out now surpass the 1GB mark.

And various social media apps have fairly large local caches. Examples include instagram, tumblr, and vine.

So if you're just using a bunch of cloud services you don't need a lot of space, but not everyone uses their mobile that way.