Because: Comcast only charges one modem rental fee( when phone and hsi). That has been part of the confirmation close for years. Such as, if you currently rent your cable modem, there is no extra charge for the EMTA. If you own your cable (edit-modem), a $.... charge will apply for the EMTA.
reply to Tobin Yes, you said a non-voice modem. I'm assuming that you are not using the phone portion of the triple play? Many older customers do not have a computer but get the TPlay, (through various providers) for cost, as do consumers who are not using the phone. If you rent an EMTA, in many packages, there is a charge. Same with certain packages, (again, all providers) might include AnyRoom, Whole Room, etc. DVR equipment/or outlet fee, HD, in the cost.