From what I know that's pretty much correct Zoodiver. Black Diamonds are collected from a certain region (the Sao Felix area of the Xingu, I think). Regular (classic) leo, and BD leo are still the same species. BD are regarded as higher quality because of the brighter white spots, and more of them. It seems to me to be the same difference between a "AAA king royal" marble, and a plain Jane marble. Same rays, just some look better and demand a higher price.
Now someone please correct me if I'm wrong because I personally do not own any leos at all, but from everything I've read on this site, and others, this is how it appears to be.
Personally I like the look of "classic" leos a little more because there is more black than spotting.