Simplest explaination is because the PVR is a network service provided by MTS. Not just a hard drive in a box like Shaw. Even if you purchased the VIP1216 (which may be possible in the future), it still costs MTS to manage the PVR service on it for you.I would rather buy the PVR for $500 then have to spend 8 extra dollars a month just to use the PVR features. Why is MTS charging for there PVR service and why is there not an option to buy the PVR?
This might explain the PVR better:
While the "total home dvr" as ATT calls it isn't available on MTS, it's expected to be in the future.
Owning it also creates a number of legal problems as well that would need to be worked through (everything from purchase, inventory and repair, to signing VoD contracts with big picture companies who want to ensure there is a full DRM solution end-to-end).