This is an interesting perspective! One thing to note is that you never have to import images and other assets into js to express that as a dependency!!
One of the coolest features about webpack is its community plugins such as html-webpack-plugin. For example through html-loader and html-webpack-plugin, you can specify in your index.html _template_ an image src or src set, this also tells html-loader to express those URLs as webpack dependencies allowing you to use image and file loaders!!
Do people often do this? I'm not sure. That's one of our main goals with webpack (2) is to provide education on different ways to approach different scenarios through our new documentation. When you don't let webpack manage all of your dependencies (code and non-code) you significantly lose out on a wealth of features for PWA, and PRPL standards.
So in the end? Maybe I am a bit biased ;) but I definitely disagree with the premise that you let other build tools handle other assets.