Your definition of plenum rated cabling is quite accurate - in commercial installations, it is required when the cabling is run exposed in a ceiling space that is used as a return air plenum (the ceiling void is used as a duct, reducing sheet metal cost and saving always-precious ceiling space). Attics and crawlspaces in homes are usually not used as plenums, but there can be cases where wall spaces are used for return air or attics serve as plenums. (There can also be cases where it wasn't intended to be a plenum but ended up that way, such as my crawlspace when we bought the house a year or so ago - previous owner had to have all the supply ductwork re-hung and sealed back up because it had fallen off the floor joists and was dumping into the crawlspace more places than it was reaching the supply registers.) I'm not sure how picky residential code is about requiring plenum-rated cable, but it's not a bad idea to use it if you can get your hands on some.