What has this to do with users? Users don't care about code.
In large companies, a lot of developers work on the same piece of code over the time. In large companies, only few (most likely nobody) know every single line and why it's there. Developers have to fix code of others, fix code that no one knows about. Old developers depart and take their knowledge with them. New developers come and have to understand what's going on.
Absolutely the same with open-source projects. In fact, these problems are even more important in open-source projects, because you can't just walk to a senior developer a few meters away and ask about some piece of code. It's important as ever to make it easier for people to understand code.
We aren't talking about yii developers only, but about all developers how write applications using it, extensions for it etc. More likely than not, most developers look at the code to understand details, some of which aren't covered in the documentation.
Hahaha. Remove “extends Controller” from any of your controllers and see the result. You'll see a generic error “Unable to resolve the request "controller/action"”. It'll take ages to understand what you've forgotten. (Silently returning null in these important cases is a bad design decision.)
What are “fw files”?
Let's look at our competitors.
https://github.com/s.../HttpKernel.php — pretty much only private functions, with comments
https://github.com/s...lerResolver.php — that's how they're getting controllers