If you are the type of person to just ride your bike fast in all weather, never clean it, and are largely oblivious to signs of trouble as long as the damn thing still moves under it's own power...than yeah, you better replace them a hell of a lot more often than every 50 years. I don't see anybody on this site behaving like that. But there is little real reason to throw away perfectly good bearings. It's easy to check rears every time you service your chain and that should remind you to check out the fronts too. Fortunately, quality replacements are still widely available. Not much point in chucking perfectly good old original bearings that usually still work fine and replacing with chinesium that is not gonna last. And be careful buying from a bearing house. Bearings come in a wide variety of tolerances for any given size. Tighter tolerance may be better initially, but any contamination is gonna wreck it rapidly. A looser tolerance may be damaged by impacts and side loads. Just some of the reasons to confirm "If it ain't broke, don't fix it."