I don't doubt it, but I get so frustrated that I need to buy a bigger iPhone to get the best camera. I just don't want that gigantic phone, but I do want the best camera possible.Almost certain to differentiate in 2019 when the Plus gets a triple camera system
And I'm sure there are several reasons Apple does this:
1) The newer technology is larger, so takes an extra year to shrink it a bit more before adding to smaller iPhone
2) Apple is Apple
3) Apple wants camera nuts like me to buy the biggest model, which gives them the most money (see 2 above).