Not adding 4GB is a little disappointing. I really haven't seen anything (yet) that makes me want to upgrade my 128 GB 7 Plus, which is still the best iPhone I've ever owned.
If you know how iOS on iPhone works, why 4GB instead of 3GB?
If Apple made it 4GB, would you cry for 5 or 6GB?
Point being, with iOS & iPhone, the need for RAM is not the same as it is with Android equivalents. One system (iOS) is hardware optimised, the other (Android) is a mess, and bloated by OEMs.