And neither is your explanation. Perhaps I should have said a lot of myths exist about what actually happens during the 10 day period.
Over the first 10 days all that is set is the MSR for the line and I am sure I do not need to expand on what that is.
Where you go wrong is that you assert that any drop of connection will result in a noise margin increase, multiple reboots are needed for this to actually happen in a short period. Why? So people with USB modems don't get margins at 15dB all the time, and to allow people to turn off kit at night.
If leaving the modem on solidly for 10 days to avoid margin changes, what happens at the end of the 10 days. The processes that alter the margin still continue don't they. Just that the MSR and FTR are set.
Your suggestion will leave people with extensions not working also, i.e. surely people should either tidy up the wiring or just use the kit in the same place as they normally would.