Valve springs are easy and cheap to replace and can be done without pulling the heads, they typically start breaking around 100,000-150,000 miles and just because someone somewhere rebuilt the engine does not mean they were replaced then if they were not broken yet. The only time I have seen seats fall out is if they fell out when the engine overheated. Rods can randomly break on 03-08 hemis and I have seen them go between 90,000 and 300,000 without breaking, seems totally random. I have a bucket of broken rods and bearings mostly look brand new.
I am not causing global warming, I am just trying to hold off a impending Ice Age!