Enjoyable article and really cool graphic. However, Miller’s Law (7±2) has been debunked for quite some time now. Do a Google search for “Miller’s law debunked,” skip the Wikipedia results, and you’ll see everything from design blogs to psychology journals addressing this myth. Here is what Miller himself said: “The point was that 7 was a limit for the discrimination of unidimensional stimuli (pitches, loudness, brightness, etc.).”
Even if 7±2 were true, it has very little to do with web or product design. Unless you’re looking up a phone number, when does a site or app ever ask you to hold 5 to 9 items in working memory? We’re hunter-gatherers who generally try to remember where to find the information we’re looking for, not the information itself. For example, we don’t need to memorize the complete list of menu items in a browser’s File menu, but when we want “Save as…” we know that’s where to look.