It's limited by the distance and quality of the copper connecting you to their system.
The only thing that can improve this limit is pulling a new wire. The other providers can't do anything different because their ADSL would be piggybacking of the exact same physical wire.
If someone's going to pull new wire, then there's no reason to not make it an optic wire and skip the copper, since you can provide all services (including landline phone) over that.
So yes, of course, in that sense nobody's investing in the copper plain old telephone system, and never ever will be.
The only thing that can improve this limit is pulling a new wire. The other providers can't do anything different because their ADSL would be piggybacking of the exact same physical wire.
If someone's going to pull new wire, then there's no reason to not make it an optic wire and skip the copper, since you can provide all services (including landline phone) over that.
So yes, of course, in that sense nobody's investing in the copper plain old telephone system, and never ever will be.