My whole plumbing system would seize up without a water softener. Especially the shower heads with their tiny holes. As it is with a 3k+ softener we get some of the rain head holes clogging. I can't see how the water heater wouldn't suffer the same fate from hard water. The minerals would build at the bottom of the tank and you would be heating through all that scale. Should always take a bucket off the bottom every month.
jonnyb: I go in there like PICASSO and toss the glue everywhere, I don't care what house I'm on.