Originally Posted by Bouville
There is no common sense that you are comparing a one single element with part of another entity. Let's say Black Sabbath and Metallica are two independent entities but what you are doing is partitioning Black Sabbath into different entities, what is not clear is what criteria are you using, replacement of singer? replacement of any individual that belonged to the band? If you do that to Sabbath, you should do that to Metallica as well.
It is just a matter of plain statistics.
Considering that the band is called Heaven and Hell, and not Black Sabbath, it seems the act of "partitioning...into different entities" is pretty much a given. Metallica is still Metallica after all, and their most identifying features -- lead vocalist, main songwriters, 3/4 band members -- haven't changed. I don't think it's completely arbitrary to assert that Sabbath without Ozzy or Bill Ward is just a wee bit more "changed" than Metallica without Cliff Burton.