With a satellite dish, each box has to have a separate cable running from the dish head.
Additionally, Sky+ boxes need two cables.
When you move from analogue to digital satellite the new dish is in a different position because it's pointing at a different satellite.
I don't know about Cable, but I think it's the same as satellite, you can't have a distribution amp in the house, each set top box needs a separate feed from the outside box.
I can't swear for the gas pipes, but I would imagine it's easier & cheaper to route pipes outside the house than to shift all the furniture, rip up the laminate flooring, then lift the floor boards, route the new pipes round the house, then put the whole lot back again...