I would argue that that's a failure of the thermostat. It absolutely needs to have a dumber fallback mechanism, not just for new residents, but for the current ones. (What if my internet goes down? What if the cat pees on my router?)
More seriously though, this is a major pet peeve of mine. Many of these devices will also become completely unusable when the manufacturer decides to terminate the service. This is a big reason why I hesitate to pay for products that don't adhere to open standards, and allow for local/offline use as a primary mode.
This has got to win HN today for the most HNist of comments. ;)
Ditto for stuff like Roombas. I've noticed all the new ones have their schedules set via an app. WTF? My current one has buttons and that works just fine. I'm seriously thinking of getting a spare now.
Smartphones are great solution for controlling a lot of things, but it seems like we're in a place where people stupidly think it's the solution to control all things.