The only time that a 75 Ohm terminator really makes a difference with Freeview is with a distribution amp that includes a "full" A.K.A. "full power" output. This is the feeder connection to cascade a second distribution amp. The standard distribution amp outputs should be well enough isolated from each other that individual termination isn't required.
Sky: Nah. For a start, the LNB (or Quad LNB in most cases) requires phantom power from a satellite receiver on each of its outputs before it becomes active. If there's nothing connected in the lounge on the other end of the leads going to the LNB then the LNB is inert. I've been to more homes than I can possibly recall where the owner/tenant has binned-off satellite. The output leads sit there unused. I've yet to come across a situation where it has caused a noticeable problem.
The caveat to both cases above is poor quality or broken cable shielding. If there's a complete discontinuity in a live feeder cable then that might be an ingress or egress point for interference.
If you feel happier terminating, then go ahead. It won't hurt. It's just a little money and time. Personally I wouldn't bother with the LNB connections though, as without power then each LNB module is dead.
Virgin Media is a different case because the cable connects back to the VM network. Best practise is to terminate unused outputs mostly because it's a path back on to the network for noise. That said though, I've been to plenty of homes that used to have VM, or Cable & Wireless, or Nynex but they binned off the gear. I can't recall seeing much evidence of termination and don't recall anyone of the home owners telling me tales of how VM hunted them down to get the cable terminators fitted.
If you're worried about the parallel cables then either terminate the end of the VM cable, or disconnect it at the splitter point before it branches off and then terminate there instead.
