Their original installation standards dictated that only the 1216 be wired with cat5, and all other secondary set top boxes be wired via coax.
Maybe a year or two ago, they changed it so that all the STB's can be on cat5. But they're very strict in that they can't be wired off a customer's router, only the MTS router. And in a case where there's more STB's than LAN ports, an MTS supplied D-Link gigabit switch is installed. BUT they don't want any internet connections plugged in at the same time on the switch.
Authorized Service Provider (Contractor) for MTS Allstream. Any views expressed are my own.