Ask a different chef and you'd get a different answer. Half of the stuff TV chef's come out with is just their personal preference - you'll notice they quite often contradict each other so they can't all always be right!
I manage to cook delicious steak using a cast iron griddle pan.
Whereas I cook much better steaks using a flat pan. Personal preference, that's all there really is to it. However, I think you'd get a better malliad reaction using a flat pan.