The "Dawn Of The Dead" was a movie... that's the only difference. People paid to see it in the theatre. If they walked out after that scene, oh well. But with a tv series, pushing the envelope with a scene like a baby zombie sucking on a severed finger paci would probably not fare well w/ most viewers.
Plus, there's good ol' censorship to consider. I don't know about AMC, but most cable networks would put the kabosh on it and request a scene rewrite. I honestly wouldn't get uber twitchy by seeing something along those lines, but it would make me a little uncomfortable.