Briggs has been using this concept for a few years. If you want to change the oil go ahead. The concept behind it is by replacing 20% of the volume of oil, which is the difference between the add and full marks on the dipstick, you will replenish the additives to keep the oil within operational standards. The requirements behind meeting this require regular maintenance of the spark plug and air filter.
Now the whole thing comes down to most people don't change their pushmower oil anyway and this has been going on forever. And the issue with the no change oil is the people that don't change their oil also don't service the air filter or spark plug.