Anyone who've managed even a modest amount of servers with ECC RAM for a reasonable amount of time has surely seen ECC events in their hardware logs. Most of these are one-time errors that never happen again on the same server, ever.
Without ECC these errors would have unknown consequences. They could happen in some unused region of memory, or they could happen in a dirty page in the filesystem cache. It's not fun to discover that your filesystem has been silently corrupted a unknown time after the fact.
Maybe Google doesn't need ECC. Their data is duplicated across several machines and it's extremely unlikely that a few corrupt servers would lead to any data loss.
However, on a smaller scale (and just like RAID) it's cheaper to have ECC than add more servers for extra redundancy.
Without ECC these errors would have unknown consequences. They could happen in some unused region of memory, or they could happen in a dirty page in the filesystem cache. It's not fun to discover that your filesystem has been silently corrupted a unknown time after the fact.
Maybe Google doesn't need ECC. Their data is duplicated across several machines and it's extremely unlikely that a few corrupt servers would lead to any data loss.
However, on a smaller scale (and just like RAID) it's cheaper to have ECC than add more servers for extra redundancy.