Seth Godin's blog posts are short and authoritative.
There are no extra or needlessly long words, and his writing flows well.
He delivers high value per minute spent reading by communicating his insights concisely. He is not in love with the sound of his own voice, and he does not write for the sake of writing.
He respects his reader's time, and as a result his posts are more worth reading.
Of course, as the old saying goes, simplicity lies on the far side of complexity.
It's easy to write a lot, and difficult to write just a little.
Concision is a virtue that must be cultivated with effort over time. It is a product of intentionality and clarity, both about what is being communicated and about why it is being communicated.
P.S. Seth isn't the only writer who talks about this – Rob FitzPatrick touts value per word in his book Write Useful Books, and Stephen King is known for his phrase "kill your darlings" (avoid conflict of interest between writing nice things and saying important things concisely).