Not true at all. I actually did speak to a 16GB owner this past weekend (my 13 year old son). He told me he browses the web and watches stuff on YouTube and that he's never had space issues and didn't need anything more (though I got him the 64GB anyway just in case). I'm also friends with a number of people with 16GB who have no issues.
For us power users, we can't fathom how anyone could possibly make a mere 16GB work (my phone and pad are 128GB). But trust me, they exist. And in larger numbers than anyone gives them credit for. They just aren't the type of users who typically join sites like this (though I've seen a few here who say 16GB is more than enough for them).
Not everyone out there uses their devices as mini computers and not everyone out there actually needs or desires all that memory.
I still wonder about that though many have to and get by with 16GB. My middle daughter was complaining hers was acting "wonky" - she is a FB fanatic. When I looked her "Other" was just under 4GB in size . After restoring it worked good enough for her. I suspect she will be back for another fix.