Top tier Indian / Sri Lankan black tea is always whole leaf. I would argue that a top tier broken orange pekoe easily trounces any OP1, but broken teas tend to be much more bitter than similarly ranked unbroken ones.
Meanwhile Chinese black teas are virtually always sold whole leaf (e.g. http://www.teavivre.com/black-tea/). On the other hand, there's a long tradition of ground grean tea in Chinese / Japanese tea culture. During Tang and Song dynasty virtually all tea was ground and matcha is still very popular today.
So I think it's mostly down to tradition. As for why, I can only guess that with the more intense, full-bodied flavours of Indian black teas the bitterness and "dustiness" due to broken leaves isn't that noticable.