You're not getting it. You are looking at a sunny-sky situation where nothing bad ever happens. Let's look at it from my perspective, a real-world perspective: my Macbook, which was used to sync my iPhone and my wife's iPhone, was stolen last fall. So who has all of this supposedly "safe" data now? Whoever has that Macbook. Probably nothing will ever happen, but now I have that little thing in the back of my mind thinking, "Hmm, if that guy happens to read about this and happens to still have it, he could theoretically track our normal daily movements." In other words, he'd know our daily routine - you know, most people have a routine and stick to it and don't think a second thing about it. Conceivably, he could come back and strike again because he has a good feel of when we're not there. I'd say the likelihood of this happening is extremely low. But it could happen because of this. (And we know the Macbook was used for a long, long time because of Zumocast - had it on our iPhones and her computer and saw him logged in all the time, starting a couple days after he stole it. Was actually able to recover some family videos that way, actually.)
That's what you don't get. People shouldn't even have to worry about this. That kind of data shouldn't be available, period. PERIOD. And don't tell me to encrypt my iPhone backups, that's water under the bridge. Why doesn't iTunes encrypt them automatically, hmm? There's no need for any of this.