I'm failing to come up with a link at the moment, but I remember a widely circulated bit of folklore about how an unnamed engineer within Google set up a cronjob that anonymously e-mailed the entire team a single number every day. After a while people figured out that the number was the byte count of the front page, the implication was that it was a metric that needed to be watched carefully.
http://blip.tv/oreilly-velocity-conference/velocity-09-maris...
Just watch from 1:00 to 2:00 -> One Minute will answer the question.
Here she tells the story, how the first Google Design came to live. It is quite interesting. It seems, that minimalism wasn't a rational choice and that it came to stay only, because the data proofed it to be the right lucky choice.
I can understand, that the minimalistic homepage was a point of pride. I would be proud, to minify the homepage of the company I work for.
As for the world's simplest homepage, that was the reason I switched from AltaVista to Google in the first place. I only started noticing the better search results after I switched to avoid the clutter.
They just realised that users came to google to perform a single, clearly defined task and decided the home page should reflect that.
I wouldn't argue it was "respect for minimalism" but it was respect for functional simplicity.
That said, I have trouble believing that changing the buttons from labels to icons could have possibly tested as an improvement. I'm with the OP; I have to mouse over every button and read the tooltip to find the Report Spam one.
http://jasoncrawford.org/2012/04/how-to-cope-with-the-gmail-...
It shows how to: get rid of "importance" markers, add some contrast back to the colors, remove superfluous whitespace, and most importantly, change the impenetrable icons back to text.
