As I understand it, they mostly did this for themselves. A change of one pixel doesn't concern any user, but it communicates the pride you take in your work.
Wouldn't say so. All these people do the best work they can - the average consumer might not consciously tell the difference, but they will notice carelessness, at least subconsciously.
Companies spend loads of money on Corporate Fonts. Most consumers will tell you that they can't tell apart Arial and any other sans-serif font; yet many companies decide that a proprietary font is a vital identity asset. Doesn't that say a lot about the meaning of typography?
The Siemens Sans font [1] is particularly fascinating: It is a very subtle modification of the ubiquitous Frutiger font [2]; most people would probably tell you that even Frutiger looks like Arial too them. And yet, Siemens spent loads of money on Siemens Sans Global, a version that "includes all of the world’s major script systems". Personally, I think that Siemens Sans is maybe the most beautiful sans-serif font ever designed. See for yourself: Do you feel a difference?
Is it valuable for programmers to discuss and refactor code to maintain a consistent casing pattern?
Is it valuable for writers to edit books to make sure they use consistent language throughout?
Is it valuable for industrial designers to iterate on the amount of tactile feedback a dial gives?
Is it valuable for musicians to continue to tweak their guitar until they get it to just the right tone for a song?
If none of those ring a bell, keep looking until you find a craft that you feel you have a strong control of, and then find the equivalent comparison. I guarantee one exists for every craft.
It's very easy for people unfamiliar with a craft to belittle refinement as useless, but only because they have an underdeveloped sense of the impact of the craft on how users/readers/listeners make decisions.