Actually this isn't the case. Star Choice and Bell use two different sections of the KU-Band which have different uses.
Star Choice uses the Anik satellites which operate in the "lower" FSS KU-Band and use lower power typically around 100watts per TP. Satellites in the FSS KU-Band (I don't remember what the letters FSS stand for at the moment) are intended for the reception, distribution, and use of both business and residential customers. Users typically are television networks, cable channels, program distributors, radio stations, telephone providers, and many more. The satellites on KU-Band FSS typically cover wide areas for both domestic and international users. Star Choice is just one company using the Anik satellites. CBC uses several Ku-Band transponders where they need the satellite's wide coverage over North America, and there are several occassional US users.
ExpressVu uses the Nimiq satellites which operate in the DBS (Direct Broadcast Satellite) or BSS (as it is known in the rest of the world) portion of the "upper" KU-Band. These satellites are higher powered than their FSS cousins, typically 200+ watts per transponder. This higher power enables the use of smaller dishes and to lessen rain fade which becomes worse as you go up in frequency. Because these satellites are for direct broadcast to consumers the signals can be narrowed to cover the area of the entended customers. In this case Canada.