These are bit level errors. So instead of losing a bit or two, you lose a massive chunk. That's the difference between a strange character in your Doc file and losing the whole thing.
I think it's 128 bits for truecrypt, although internet searches point to many people using higher (1024 and 4096).
And if the bit level error rates are as high as he says, looks bad.
If the hard disk detects the bit error, it will return an I/O error instead of the corrupt data. Likewise, ZFS will not return corrupt data. So there are plenty of cases where bit errors are promoted to block errors. I can understand the desire to minimize propagation of corruption, but I'd rather just use RAID.