Given what little I understand about fibre can someone explain

[#1]

http://www.theregister.co.uk/2014/12/12/bt_infinity_working_to_fix_the_problem_after_three_days_of_o...
Why aren't all users of BT Openreach Fibre affected
If it is specific to BT Retail why doesn't it affect ADSL users as well as BT Infinity
The users don't seem very happy https://community.bt.com/t5/BT-Infinity-Speed-Connection/BT-Infinity-issues-for-the-last-few-days/td...

[#2]

It depends where in the network the fault lies, I don't know enough about the issue to decipher that part unfortunately.