Backing up your wallet after every transaction is pure madness. Consider small marketplaces or "banks", that might receive several transactions per minute. If their server goes boom, the wallet and the backup might be both gone.
On Linux/UNIX there are network filesystems such as NFS and CODA, which can give you multiple backups on many servers at once. Everything everywhere cannot just go "boom" all in the same time.
Not saying about ZFS, SAN/RAID disk arrays, and lots of other technologies which give you multiple data redundancy. You can have as many backup servers as you want... possibilities are endless.
Anyway, this is not really a problem, because modern banks all use electronic currencies already, and if their computer systems failed, people would lose money the same way as they would lose bitcoins...