I can't remember if they said ABC was going to carry it or not. Not sure why the any of them are not carrying it. The republican response should be a big draw, it might be pretty funny.
That hasn't stopped them any other time I know of. They didn't carry one of HW's speeches because they said it was just going to be a campaign ad for free, not a real policy speech. I'm pretty sure this had to something to with policy.