This is false. My Ubuntu desktop handles 4K DPI scaling perfectly, while attached to a 1440p with normal scaling as well. On the other hand my 2012 MacBook scales extremely weird when connected to a 4K display through HDMI.
Why do you need a new Macbook when your machine probably does everything? The specs between a 2016 and 2013 are negligible for web browsing and programming. Unless you're doing heavy video editing or 3D rendering..
So many people upgrading notebooks when they don't need to.
Because it's expensive and is a sidegrade to anyone who owns a MacBook Pro from 2012 and newer. I don't know why any developer would upgrade their MacBook Pro if they bought one in the last few years.
I have a 2012 15" MacBook Pro Retina. Upgrading to the new one doesn't feel like it would be much of an upgrade. My current notebook does everything I need (ST3, web, music).
I think when MacBook Pros have 4K screens, or better yet, OLED screens, I will upgrade. I'm thinking that will be 2018 or 2019.