That struck me as odd too. At least 2 player online is still confirmed. You cannot play Reach with 3 or 4 players online for anything other than a complete laugh.
I agree with you. Rich cool people play with one screen liek Richie Rich. Cool kids who are charitable play with 2 player split screen, like BJ McKay and his Best Friend Bear. Brady Bunch maniacs do four player split screen and I assume they fail at SWAT a lot. BUT - Halo 4 still supports four player split screen for MP - Brad was conflating co-op, I suspect.