There is an exception to this observation about senior management: Andy Grove used to sit in a cubicle. It was a big cubicle in a labyrinth of his assistants' cubicles.
There's an exception to almost everything. Intel was a famous exception on cubicles for upper management; the CEO had a cubicle just like normal employees (except the CEO's was bigger and not accessible from the aisle of course). The CEO also didn't have his own special floor, special bathroom, special elevator, etc.
It didn't make cubicle farms any better though.