Your line of questioning is great. And it's something that drives me up the wall that designers don't engage with these questions better. Here's someone from DesignerNews on your comments:

"Here's what the left-brainers have to think about such a well though-out and through design process..."

It's hinging on the effort that went into the process, which is by all means extensive and impressive. Its' defensive. But I think your line of questioning is extremely important and I'm a designer, so I'll give it a bash with explaining why they did this.

I don't think you could ever back up with numbers that these changes 'matter' to users. Any research that could be done would, in the words of someone better than I – be used like a drunk uses a lamp post. For support, not illumination.

At the end of the day, I'm inclined to agree that these changes are negligible for users. What this is more a case of is Facebook deciding they care about the craft and quality of the visual design in their product. Regardless of if users give a toss. The change isn't quantifiable in numbers. It will most likely not change the bottom line of the company.

But what it does do, is communicate that Facebook cares about visual design craft. This is part of branding. Deciding they care about these things, to have the image of the company they want.

These changes are on par with Apple choosing to make a glass staircase in their stores. It's like Twitter choosing the colour of their office furniture, it's like any other company implementing anything that does not directly or clearly affect returns or is quantifiable in numbers. Simply put, it's a culture thing. They've decided they care about visual design craft and so they put money into it so they can have high quality visual design craft. And they have done that here – this is high quality.

Oh man, "the left-brainers"? What happened to "Good design makes a product useful/understandable"? If it does either of those things, the effect would be measurable. I don't have any trouble believing that investing time getting the design right translates into better engagement or sales or whatever metric, and you should be able to hold your work up to the light. Writing off a provocative but genuine line of questioning such as jlarocco's is pretty much relegating yourself to the echo chamber.

Apple's computer products are on par and often mediocre with the last few years of Windows-based computers. Retina is on match from other vendors for less. Many retailers offer price-for-price better performance, better graphics support, as much or more memory.

Apple offers a fantastic tactile experience and OS X -- the user experience ecosystem is the big sell for them, which is why their operating system has been a loss-leader for so long. A similarly priced Dell XPS 13" is going to out-perform a new MacBook pretty much everywhere but battery life (which it misses by something like an hour), but the Apple is the more attractive buy because of OS X and the joy of using it.

It's demonstrated and acknowledged, through profit and market dominance industry-wide, that there's more to life than tech specs, and that more is user experience. There's really little else to say on it...

You''d have thought on Hacker News of all places at least one person would pop up saying that they had AB tested user engagement with consistent and inconsistent variants.