I guess 37signals hires employees that like the design of the place. i.e. personally, I really like how 37signals is designed and I wouldn't even think of putting something weird on the wall.. so in a way, 37signals let me design the place how I want it to be (clean and empty). So, by working in a clean place, I control my environment by letting it stay clean.

In contrast, working at Zappos's office, how would I be able to control my clean environment?