Unlike the other utilities the service is provided over unique lines, not a shared pipe or wire.
Not always, but that's all part of the joy of telecoms. Often lines aren't unique and are shared, ie indie telco may lease fibre from BT, VM, C&W, COLT etc and resell it. Whether that matters usually depends on what you're trying to do. If it's diversity, ordering from 2 suppliers may end up with both on the same route. If the endpoint only has a single entry, it'll be shared. Even though a dual supplier policy sounds good, in practice it can be pointless because there's no real certainty that suppliers might groom or regroom capacity and end up sharing a route. Finance types seem to like this one though because it creates an opportunity to play one supplier off against the other, or a new supplier come renewal time.*
Personally, if you really want diversity, buy it from a single provider. That way circuits can be planned and maintained to remain seperate, and that seperacy can be maintained and protected during any network shuffling.
* Sorry if I've no-bid when you've tried to do this, but unless you can control the solution, you can't provide five 9s, or really meet any of the stuff you might have put in your bid or desired SLA. It just doesn't work that way.