The installers are NOT supposed to be using coax to the PVR. Lazy a**es! There's only some situations where it's an absolute last resort if cat5e can't be ran. I've only done it once AND only after talking to one of the quality control techs at MTS. This was in a house that was almost new, so the coax was RG6 and 99% perfect.
The PVR probably demands a lot of bandwidth when sending recorded content to the non-PVR boxes, that's probably why they want cat5e.