The point was to show what this library is capable of, so that people with the imagination of your imaginary co-worker could extrapolate its usefulness to real world applications.
I have built 3 large applications using kea, and at that scale all these features come in handy.
The problem with Slider is that it doesn't readily extrapolate into anything bigger. To put it another way, it's not the embryo of any real world web app.
I feel this indicates a larger problem with present-day web dev: due to the complexity of client and server stacks, it's really hard to come up with a self-contained example app that makes any sense as a starting point.
Looking back some 20 years, one could look at the example apps from the Win32, Classic MacOS and OpenStep SDKs, and come out with a solid feel for what it's like to build an app on each platform.
Today, I could compare the provided examples from twelve different JavaScript frameworks, and I wouldn't feel any closer to understanding their strengths.