Kind of but to elaborate more, the main reason isj ust simple, less work less cable...
None of this matters much though, even with your grounding. You can ground to any water line or if need be put in a ground rod to ground to.
Heres what you want to do (imo)
1) Like I said b4, run 2 dedicated lines from your panel to each room leaving slack at both points (about 3 ft) That way if you ever want DVR's you have both lines (they require two independent lines.
2) As far as lines going from the panel room out to the dish, you can ground it in there if you want, since its bare walls, you can run a ground wire into the wall plugs ground, its your best bet. They make ground blocks with 4 barrels on them.
3) as far as placement and where to run these lines, your Sate needs a clear shot of the Southwestern sky @ a 37 degree angle (not that steep) Hows your SW view? any trees? If not then put it as close to your AV panel room you can, run them down the side of your house, I guess if you want to use conduit you can.. no reason though, they will be protected from UV and last forever. I think they are called "Jakes"?? The 90 degree elbows to go into your house, also, that gray pvc is for electrical.