To be honest, I've watched the BBC footage half a dozen times, including the freeze frame, and between the crappy camera angle and Andy Rose in the way, I still couldn't tell you from that alone whether the whole of the ball was over the whole of the line at the moment he headed it, even though my initial full-speed reaction was that it must've been. So while I'd have expected them to at least have another look at it on the programme, they probably wouldn't have been able to say much other than "I dunno" either, which doesn't make for a riveting discussion.
Rightly or wrongly, the fact that it ultimately didn't affect the result probably bumped it down their priority list, too.