I run OpenHAB at home (and have tried HA), but setting all this up is not in the wheelhouse of the majority of people. Doing the in-home setup is difficult enough, but safely exposing it to the internet is not something I'd ever ask a non-technical person to do.

Meanwhile, you just swap your old thermostat with the Nest, tell it how to get to your wifi, install an app on your phone, and you're done.

Yeah that's what a lot of the responses in this thread don't get or dismiss. These things could be run in a much more privacy protecting way but that comes with all sorts of configuration and setup headaches that most people don't want to deal with. And being able to access the devices from anywhere is a feature most people want even if it's only useful occasionally and a central API running all interactions means if it works while you're home it will work anywhere rather than it working while you're home then not working because something something DynDNS/NAT.

I think you're overestimating how difficult it is to setup a smart device with something like Nabu Casa's Home Assistant Cloud.

And youre over estimating the technical literacy of the average person. This is the first time I've heard of nabu casa, I just checked out their website and they're immediately talking about yaml, I've browsed every page I can see and I can't see anything about setting it up. Another labe mentionrd docker and JWT as troubleshooting steps - that's too much for 99.99999% of people to ever use.

I'm under no delusion that the average person can, or is willing, to setup something like Home Assistant.

I was answering a question posted on HN, where the assumption that the average HN user is capable of fiddling with hardware and software is usually valid.