>> "Most places are wired with one phone line, and one cable line. That phone line is generally owned by one specific phone company, and that cable line is generally owned by one specific cable provider."

That seems to be where things differ. My phone line is owned by BT but I can still order internet through a different company. I pay that company an extra £10-15 per month for line rental (so I guess BT, even though they own the line chooses/or has to rent it to others).