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Well what you found is true, but only half in Japanese cars which is usually hooked to expansion bottles. If ever you have a chance then clean your expansion bottle and see the amount of sand it has. Though that part is loosely designed to let air out and suck/return the coolant means it also inhale the atmospheric sand and dirt and keep churning inside the bottle and from time to time that sand makes it way to the radiator and sit nicely inside the core and block them overtime. If you clean your coolant expansion bottle every month and top up with fresh coolant, then you can delay the radiator core cleaning from every year to once in 2 years easily.