Im pretty sure the whole leaves are broken through CTC, then sorted according to size, so the main point is the quality of the original leaves, not the size of the resulting leaves.
It seems a lot of african teas are "big fannings", even though theyre high quality made from clonal plants. However i don't know where to buy them, except a local danish dealer which has one type which is not exceptional quality.
Here is a image of a broken leaf Assam, which i will probably try at some point:
It's graded as FTGFBOP, notice the B for Broken. It's also more expensive than most of the whole leaf Assam's sold on the same site.
Edit: I just checked my tea book, and it seems that fannings and dust are in the same category, but Fannings are larger than dust and probably also better quality.
Oh and a final point: When i say a lot of people prefer broken, i don't mean the majority. Even 10-20% of informed black tea drinkers is still a lot of people