I work for one of those businesses and we were affected. The reason we didn't have a backup line, is because the other major ISP (Virgin) doesn't have its fibre in our region. Therefore, BT is our only option.
Edit: you could also consider a backup line from an LLU provider. You still have the copper as a single point of failure, and perhaps power at the exchange, but the infrastructure is different.
Edit: you could also consider a backup line from an LLU provider. You still have the copper as a single point of failure, and perhaps power at the exchange, but the infrastructure is different.