Sub question: Would you care if you lost a few blocks of data? Bit rot is a serious concern but the problem is an isolated one. If I lost a single photo on my computer I may be lightly upset, but no where near as upset as losing all the data on my drive.
Like you said, it depends which block.
I could have a corrupt block in the middle of a movie file and not even notice, but if I lost a block near the beginning of a large compressed archive file, I may lose the entire archive -- and if it's silent corruption undetected by the filesystem or disk drive, it may be propagated to all of my backups before it's discovered.
I'd rather have the drive fail entirely versus slow undetected block corruption.