[jpollock]

Systems, particularly safety-critical systems, are tested in specific configurations (inputs, users, integrations).

If you change the configuration, you encounter the possibility of finding new bugs. When someone's life is tethered to the device, this will make engineers (and lawyers) properly twitchy.

For a perfect example of this, have a look at the the Ariane 5 [1]. Existing software was used in a new configuration and when it encountered an untested condition the software crashed, resulting in the rocket self-destructing.

Now, consider, you're adding bluetooth to a safety critical device - this is a protocol stack where people can't get their phone to connect to their car, and my Android phone occasionally needs to be rebooted before it will connect to my headphones.

[1] https://en.wikipedia.org/wiki/Cluster_(spacecraft)#Launch_fa...