As far as I know, and I could easily be wrong, the idea behind most plenum rated cables is to provide some time before the fire burns through the cable, thus providing your systems an extra bit of time to continue working. Very important for fire alarm systems and the like.
As far as standards go for data cabling in commercial building, if a building is combustible (wood framed) you don't need to protect your cables in any way. They get strung through the ceiling space using hooks, and no conduit is needed even behind the walls. In a non-combustible building all of your data cabling must be in cable tray and conduit throughout the ceiling and behind walls. I would imagine the same sort of rules would apply for residential buildings.
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