I can't even understand what the article is trying to prove (they say a good article is one you can skim through and grasp the point it is making), so looks like the writer is breaking guidelines.
Have you ever noticed how a Mac running Tiger or Leopard has maybe ... what... five or six different kinds of windows, or even more, depending on what you count? And yet, to the average consumer, it actually looks like a coherent whole, and seems more consistent than Windows XP does with essentially just one kind of window? Or how OS X looks cleaner and more refined than Linux in spite of the development of some very complicated Linux theme packages?
There's a paradox in look and feel. It's very
natural and
easy for the brain to process information that's consistent with the real world. Your visual cortex is designed to process the kinds of perspectives, textures, and features you see in the natural world. It's harder, in contrast, for your brain to process something that is not consistent with normal reality. The paradox is that it's
easy to create something that isn't consistent with what your brain expects, but it's hard to maintain that consistency.
The HIG and related specifications are what allows for this.... OS X is visually gorgeous now, without Leopard. But it's gorgeous because, even with all the different themes and looks, a consistent
philosophy of the interface and the way it will be perceived by human users is maintained.
So I think this is important. Not in the sense that users need to make a decision about it, but in the sense that OS X can easily become increasingly less refined and uglier over time, if the consistency that makes sure you don't even notice anything might be out of place, is lost.
