I kinda thought it went like this:
WAREZ = Games from systems that are still "ALIVE" i.e. PS2, PS1, XBOX, GC, PC, GP32, NGAGE, PSP, DS, etc...
ROMS = Games from "Dead" systems i.e. SNES/SFC, Gen, NES, Atari, PCE, WS, etc...
Basically if a game is still generating/able to generate profit for...