The Greek temples were mostly destroyed by religious strife. A true testament to their strength is that the ruins of them still stand despite a thousand years of mistreatment, abandonment and earthquakes.
And I'll concede the point on the Cathedrals. But they were hardly built to be permanent static structures. However, a lot of them weren't done very well in the first place. But still, those that were built properly need a minimum of maintenance.
And yes. Angkor Wat is just awesome.