Actually, this is a fine lesson in persuasion, something that Chip and Dan Heath point out in Switch and Made to Stick; that is, reasoning that is highly concrete and visual is far more convincing and impactful than appeal to models, forecasts, spreadsheets, and schematics. I think Jobs here could have simply demanded rounded rectangles or appealed to some vague need for geometric completeness in the product, but imagine how powerful it must have been to take a walk outside and actually see how reality presented rounded rectangles at every turn, and how truly crippling the program would feel with this observation in mind if it didn't ship with the feature. The lesson is to reach beyond the world of formal logic and into the visceral world of sight and touch, where the real "aha" and gut judgments reside.

Here's another example, cited in the design and creation of the Palm Pilot:

"Jeff Hawkins, the team leader, wanted the Palm Pilot to be simple. It would handle only four things: calendars, contacts, memos, and task lists, but it would do them well. Hawkins fought feature creep by carrying around a wooden block the size of the Palm. Hawkins would pull out the wooden block to "take notes" during a meeting or "check his calendar" in the hallway. When someone would suggest another feature, Hawkins would pull out the wooden block and ask them where it would fit. Hawkins knew that the core idea of his project needed to be elegance and simplicity. In sharing this core idea, Hawkins and his team used what was, in essence, a visual proverb. The block of wood became a visual reminder to do a few things and do them well."

taken from http://www.gsb.stanford.edu/news/bmag/sbsm0702/feature_ideas...