I think they have to use Shaw only EQ Furry. Atleasts thats what I gather from their DSLReport forum. And even if you could, looks like there having some big issues with DOCSIS 3. If I had to guess, its their traffic management system. Their infrastructure is under build and over sold, so when they get a push, they have to drastically cut bandwidth to get by.
And even if you could buy your own modem, they load their own firmware, which cuts out signal levels. I guess shaw goes by the theory "The less the customer knows, the better". That kind of attitude just pisses me off. But I have to also keep in mind this is a Canada ISP. They probably just do things differently.