And then again, often people put new stereos in cars...aftermarket, etc.
Not so much, no. Modern cars have single infotainment systems that include the air conditioning, navigation, etc, all tied into one unit. An aftermarket system isn't going to be able to interface with the climate control system on different makes/models. My car is a 2004 -- over 20 years old -- and even though the stereo and the climate controls are technically separate components, they are together in the same (proprietary) section of the dash (no DIN or Double-DIN slot). Replacing the stereo means getting third-party controls for the A/C. The alternative is removing a lower storage pocket to add a installation bracket for the new stereo and having a "dead" (non-functional) factory stereo remain above.