the raison d'être for a bus stop is not to sell cellphones, purfume or clothing. It is exists to establish and protect a pickup/dropoff point. The bus stop would exist even if the no ads were ever sold for it.

On the other hand, the rambling, first-hand, poorly-worded 4 page review the latest sous vide exists solely to sell you that device. This is "content marketing". The text and graphics are inseparable from the intent to sell.

Somewhere in the middle is the Slate webpage that links to the sous vide review. It wasn't written to sell that particular appliance, yet ad revenue is very much top of mind.