Reason 1: I pay for my bank account one way or another. It's bank's responsibility to keep the system running and secure, not mine. Sometimes we just can't do everything ourselves and have to rely on others.
Reason 2: Many of us host something somewhere. How many do backups? How many of us check the backups? How many do check the backups checking process? (enter infinite recursion) You have to stop at some stage. You probably don't have enough time, or your time is not worth enough to check that.
He can recover most of his blog from the caches, because it was quite popular. I bet he'll be back with an almost complete archive in less than a week.