I see your point, but it is a little bit misleading to say developers have complete freedom to draw their UI any way they want. You can still have an app reject

I see your point, but it is a little bit misleading to say developers have complete freedom to draw their UI any way they want. You can still have an app rejected on UI grounds during review. Make an app with a crappy enough UI and it can be rejected citing the "Substandard User Interface" rule in the App Store guidelines. What constitutes the meaning of "Substandard" is of course whatever Apple wants it to be.