Source? Isn't that only true due to the fact that most people do not change thermostats in homes/apartments/condos they move into, or when they change HVAC systems?
I'm not so sure. For a home DIYer, changing a thermostat is a pretty simple project. I bought a nice programmable unit a few years ago to replace the old mechanical one, and the entire process took maybe 20 minutes. It's along the lines of "attach the red wire to this screw. Attach the black one to this screw. If you have an air conditioner, put the white wire on this screw."
It didn't involve any tools beyond a screwdriver and the instructions were dead simple. I wouldn't hesitate to install another replacement unit myself.