Re: "what the hell good is it?"
Who says they'd sell all that stuff? They make a few accessories for iPods, iPhones and iPads, but mostly leave that up to third parties. Ditto for apps.
I think it is much more likely they'd sell an iWatch that relied on developers and gadget makers to help create demand for it by the products and software they created. Similar to how iTunes was never intended to make much money for Apple but to help sell iPods and later iPhones, because Apple makes 98% of its profits from hardware, and iTunes barely pays its running costs.
If it didn't use some sort of open protocol, maybe it can be broken, but why? If you don't like being in the Apple ecosystem, why would you buy an iWatch? If it is a hit, I'm sure it's functionality would be available on Android branded products eventually, and Samsung would call it S-something (too bad for them Swatch is taken)
Not sure how much market there is really for controlling your thermostat remotely, on a watch or a phone. That's mostly a geek thing, regular people want to set it and forget it. The only somewhat useful thing I can imagine is if it could track everyone so it knows when no one is home and can save energy, then returns to normal settings when one of the tracked residents is on the way home. But why would I need a watch for that?
It isn't clear to me how controlling anything using a watch is somehow better than controlling it with a phone. The guy claiming this rumor must envision a world with a lot of thermostat and appliance tweaking if he thinks the time savings not having to pull a phone from one's pocket is such a big deal Apple is basing a new product line on it.