I literally dealt with this just a few hours ago. I need a new HVAC system. I wanted the high-end model, but it will only work with their fancy cloud-connected thermostat. You cannot replace it with an off-the-shelf thermostat.

Have home automation? Sorry, you'll have to use the Internet.

I vote with my dollars, so it cost them the higher-margin sale. I also went with the mid-tier system, and grabbed a Z-Wave compatible thermostat along with it. I wonder if I'll miss the nifty variable-speed system?

I really wish everyone would stop trying to trap us into their walled gardens. Apple at least lets people write software for theirs, but the hardware/appliance manufacturers (not to mention the automotive folks) are awful about this.