[D]ata gathered using HomeKit APIs cannot be sold to advertisers or used “for purposes other than improving the user experience or hardware/software performance.” On the one hand, [HomeKit’s terms] ties in nicely with Apple’s recent focus on privacy. On the other, it may prevent potentially useful data from being collected and presented that could be used to inform laws and regulations.
iOS 8, thoroughly reviewed | Ars Technica
Why would I want my thermostat usage to “inform laws and regulations”? What good could that possibly do for me?
These terms will prevent Nest, or any Google product, from being HomeKit-compatible. Which is a good thing, since hardware companies will have a chance at becoming a successful product, without selling out their users.