Writers are desperate to come up with ideas for articles so they torture one piece of advise to make a point.
The coffee savings = comfortable retirement is a canard to make the points in the article. Without it, the authors would be repeating the same advise - research house values when you buy, learn to negotiate and research stocks/indexes.
The takeaway from the article is wrong.
"The important takeaway is how much everyday scrimping and saving you have to do to make up for an investing mistake. "
The real takeaway is that none of us can always make the best financial decisions. Making a lot of small wise financial decisions (e.g. coffee spending; cars; and other things people on this board mention) can help to off set some larger financial mistakes.
Also, the point about the coffee is to be aware on how relatively small spending decisions can add up over time, learn to track your spending so you can make informed decisions, understand compound interest, etc.
Sometimes death is not as tragic as not knowing how to live. This man knew how to live--and how to make others glad they were living. - Jack Benny at Nat King Cole's funeral