Can't they still just provide you with a "modem" and give you full IP access through that? What difference does it make if they put the modem inside our outside

Can't they still just provide you with a "modem" and give you full IP access through that? What difference does it make if they put the modem inside our outside your premises? (Eg they put a switch/DSLAM/modem into a box on the street and then they give you a cable?)