In addition, all the junk (especially those in the combustion chamber) cleaned out by Techron will also find their ways into the oil and oil filter somehow. Changing the oil after a concentrated does of Techron is just a good idea. All it requires is your timing the use of Techron.
According to your theory, then oil should stay clean for ever if the system is in perfect shape. Unfortunately, that does not happen. Oil gets dirty and its color changes to dark (especually in a diesel engine) because combustion by-products (which Techron and gasoline produces) find their ways into the oil.