Like: "I'm getting fed up of making the rich... well, richer".
"I'm getting fed up of making the rich... richer" might be grammatically ok in informal text, but a comma is definitely wrong.
But today, it's wrong.
EDIT: I like qwertox’s answer best
Source: Garner’s.
Like with any language, there are wildly varying levels of literacy. Many native English speakers know how to use commas, and many others don't. I think that shades from using them grammatically (most literate), to using them ungrammatically as a generic pause, to not using punctuation at all.
I think part of why we've shifted so strongly against their use is because if you leave it up to taste, as had previously been common, most people make poor choices.
It's funny because even as we've moved away from prescriptivism, the "rules" around comma usage have tightened and people have gotten quicker to call a given previously-common usage incorrect.
The notion that a comma is any sort of pause fell out of favor in written English in the 1800's and thankfully hasn't been back (see the second amendment as to why "a comma is a generic pause" is a bad idea). You would have to be the loosest form of descriptivist to say that this usage is close to correct, and I would question whether you would accept any grammar rule at all at that point. Many people use run-on sentences and many don't capitalize the start of sentences in very casual text, even though these are widely (universally) accepted rules.
To the extent it's "incorrect", it's in that it generated this discussion at all.
I think if the author wanted a "pause the sound while keeping the syntax flowing" mark, the ellipsis (...) would have done the trick much better. In my opinion, though, this sentence did not merit any pause between "rich" and "richer" since there's nothing surprising about that word.