I believe it mean aluminum radiators with plastic side tanks don't last forever. With good care, they're good for only about ten years. After that, the side tanks start to have a much higher failure rate. "Good care" means a flush and refill with fresh coolant every couple of years.
Poorly maintained radiators, i.e., infrequent flushes, suffer early failure due to corrosion of the aluminum or clogging of the passages.
Old style all brass radiators could last much longer if given decent care. Much as I love modern technology, I do miss brass rads. | 
Radiator rot? 
