Assuming it's anything like regular eclipse the UI probably is highly customizable.
It's more like a tiling window manager
You can choose how many of those panels you have and which tabs are in each panel and which buttons you have in your toolbars.
> The actual code takes up like 40% of the screen.
considering that many projects still have guidelines regarding line-length (something around 80-120 characters) there's only so much horizontal space you can utilize. I can easily fit two source files side by side on my monitor and still have room for additional panels.
> Is this actually what programmers want from an IDE, or just what they have come to expect?
The more you can have on the screen at the same time the fewer permutations of arrangements you need for different tasks.
If we are to extend the desktop analogy, it's a work bench with a wall of tools hanging in front of you, every individual tool within grasping distance.