Author here. The majority of non-personal emails contain some form of styling for readability. And the styling is done using CSS. The only issue with Gmail is that they force you to inline them which makes coding email very tedious.

> for readability

Really? Because I find it so much more readable if all of my emails are the same font.

Yes. Why a common man want css in their email? The so called "developers" in the article are actually spammers!

We moved to gmail to escape from spam not to get more spam.